Drugs and Heart Disease Were ‘Not Direct Causes’ of Floyd’s Death, Medical Examiner Says

Last Updated April 21, 2021, 8:03 a.m. ET

Dr. Andrew Baker said the efforts by Derek Chauvin and other officers to restrain Mr. Floyd were more than he could take.

ImagePeople visit Cup Foods in Minneapolis where George Floyd was arrested.
Credit...Joshua Rashaad McFadden for The New York Times

Follow our live updates the day after the Derek Chauvin guilty verdict.

April 9, 2021, 5:57 p.m. ET

The scene around Minneapolis as the second week of the trial comes to a close.

Reflections of a George Floyd wall memorial; a woman holds a sign near the Hennepin County Government Center; Mr. Floyd’s brother Philonise Floyd arrives for the trial; flowers and pictures on the corner near Cup Foods; the courthouse reflected in a puddle.

April 9, 2021, 5:50 p.m. ET

Takeaways from Day 10 of the Derek Chauvin trial.

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Floyd’s Cause of Death Was Homicide, Medical Examiner Says

Dr. Andrew Baker, the Hennepin County medical examiner who performed the initial autopsy of George Floyd, said that there were contributing factors to Mr. Floyd’s death but that ultimately it was homicide.

“Do you recall describing the level of fentanyl as a fatal level of a fentanyl?” “I recall describing it in other circumstances, it would be a fatal level, yes — in other circumstances.” “And you all — would you agree that one of the causes of the pulmonary edema that you communicated to the county attorneys was also fentanyl?” “Fentanyl can certainly be a cause of pulmonary edema. As I indicated earlier in previous questioning, it’s confounded by the fact that Mr. Floyd had quite a bit of CPR. And so I find the pulmonary edema much less specific “What today remains your opinion as to the cause of death for Mr. Floyd?” “So my opinion remains unchanged. It’s what I put on the death certificate last June. That’s cardiopulmonary arrest, complicating law enforcement, subdual restraint and neck compression. That was my top line, then, it would stay my top line now.” “And so we look at the other contributing conditions. Those other contributing conditions are not conditions that you consider direct causes. Is that true?” “They are not direct causes of Mr. Floyd’s death, that’s true. They’re contributing causes.” “And in terms of manner of death, you found then. and do you stand by today that the manner of death for Mr. Floyd was, as you would call it, homicide?” “Yes, I would still classify it as a homicide today.”

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Dr. Andrew Baker, the Hennepin County medical examiner who performed the initial autopsy of George Floyd, said that there were contributing factors to Mr. Floyd’s death but that ultimately it was homicide.CreditCredit...Still image, via Court TV

One of the most anticipated witnesses of Derek Chavin’s trial, the Hennepin County medical examiner who performed the initial autopsy of George Floyd, testified on Friday that while police restraint was the main cause of Mr. Floyd’s death, drug use and heart disease were contributing factors.

The medical examiner, Dr. Andrew Baker, declared Mr. Floyd’s death a homicide in his autopsy, but had made several statements leading up to the trial that could have complicated the arguments of the prosecution, particularly in relation to Mr. Floyd’s drug use. In all, his testimony maintained that Mr. Chauvin’s actions — pinning Mr. Floyd to the street for nine and a half minutes — were the primary causes of death.

Jurors also heard from Dr. Lindsey Thomas, a forensic pathologist who helped train Dr. Baker. During her testimony, Dr. Thomas said she believed that Mr. Floyd died from a deprivation of oxygen caused by the restraint of Mr. Chauvin, the former police officer charged with murdering Mr. Floyd. Here are the highlights from Day 10 of the trial.

  • Though multiple contributing factors may have contributed to Mr. Floyd’s death, Dr. Baker said he believed that the primary cause of death was the same as he wrote in his initial autopsy: “cardiopulmonary arrest complicating law enforcement subdual, restraint, and neck compression.” In simpler terms, Dr. Baker said that Mr. Floyd would not have died were if not for the actions of Mr. Chauvin. Still, he said that the compounding factors, including heart disease, played a role as well. Dr. Baker agreed with a statement from the defense that methamphetamine was hard on the heart; a toxicology report found methamphetamine and fentanyl in Mr. Floyd’s system, and pill fragments found at the scene contained the same drugs. Dr. Baker said he found no pill fragments in Mr. Floyd’s stomach.

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Credit...Court TV still image, via Associated Press
  • Mr. Floyd had a larger heart than most people, Dr. Baker said. It required more oxygen to continue pumping blood throughout the body, especially during a high-intensity situation like the one Mr. Floyd experienced when being pinned to the asphalt for more than nine minutes. “Those events are going to cause stress hormones to pour out into your body, specifically things like adrenaline. And what that adrenaline is going to do is it’s going to ask your heart to beat faster. It’s going to ask your body for more oxygen so that you can get through that altercation,” Dr. Baker said. “And in my opinion, the law enforcement subdual, restraint and the neck compression was just more than Mr. Floyd could take by virtue of those heart conditions.”

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Medical Examiner Describes George Floyd’s Heart Condition

Dr. Andrew Baker, the medical examiner for Hennepin County, said on Friday that Mr. Floyd had a heart condition that put him at a greater risk in situations with high physical stress.

Can you tell us how it is physiologically that the subdural restraint and neck compression caused Mr. Floyd’s death? In my opinion, the physiology of what was going on with Mr. Floyd on the evening of May 25th is, you’ve already seen the photographs of his coronary arteries, so that, you know, you know he had very severe underlying heart disease. I don’t know that we specifically got to it, counselor, but Mr. Floyd also had what we call hypertensive heart disease, meaning his heart weighed more than it should. So he has a heart that already needs more oxygen than a normal heart by virtue of its size. And it’s limited in its ability to step up to provide more oxygen when there is demand because of the narrowing of his coronary arteries. Now, in the context of an altercation with other people, that involves things like physical restraint, that involves things like being held to the ground, that involves things like the pain that you would incur from having your, you know, your cheek up against the asphalt and an abrasion on your shoulder, those events are going to cause stress hormones to pour out into your body, specifically things like adrenaline. And what that adrenaline is going to do is it’s going to ask your heart to beat faster. It’s going to ask your body for more oxygen, so that you can get through that altercation. And in my opinion, the law enforcement’s subdural restraint and the neck compression was just more than Mr. Floyd could take by virtue of that — those heart conditions.

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Dr. Andrew Baker, the medical examiner for Hennepin County, said on Friday that Mr. Floyd had a heart condition that put him at a greater risk in situations with high physical stress.
  • Eric J. Nelson, the attorney leading Mr. Chauvin’s defense, used his cross-examination to push back on Dr. Baker’s findings. Mr. Nelson urged him to elaborate on the fact that he found no bruises on Mr. Floyd’s back, and that the level of fentanyl that was found in Mr. Floyd’s system could have been fatal for some people. But throughout the cross-examination, Dr. Baker appeared to be uneasy with Mr. Nelson’s line of questioning. On the issue of bruising, for example, Dr. Baker said that death by asphyxiation — or the deprivation of oxygen — does not necessarily cause bruising. On the issue of drug use, Dr. Baker said the level of fentanyl that was found in Mr. Floyd’s system could be fatal in other circumstances, but that, in Mr. Floyd’s case, it was a less likely cause of death than other causes.

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Forensic Pathologist Says Physiologic Stress Contributed to Floyd’s Death

Dr. Lindsey Thomas, a forensic pathologist, testified on Friday that police restraint killed George Floyd, primarily by restricting his oxygen with a secondary effect of physiological stress on his body.

“I think a secondary mechanism in this case is what I refer to as physiologic stress, and by that I don’t mean like the stress — oh somebody’s a Type A personality, and they have a deadline at work and they’re just really stressed about it. I’m not talking about that kind of stress. I’m talking about the kind of physical stress you feel when you’re driving along and all of a sudden a car swerves right in front of you, and you slam on the brakes and you realize, oh, my gosh, if I hadn’t reacted, if that had happened a second earlier, I would have been in a potentially fatal car crash. And you can feel your heart racing. You get chemical release. You get adrenaline noradrenaline or epinephrine, norepinephrine. And those are things that make your heart race, your blood pressure go up. All of those physical things, those chemical things can cause reactions in the body that put additional stress primarily on your heart, but also on all of your body systems because your body requires your chemistry to be in very fine balance. And when there’s too much, say, lactic acid or too much, not enough, you know, not an ability to compensate for that elevated lactic acid, then all of your body organs will get into trouble.” “And so the direct cause is what? And then the secondary cause is what?” “So their sort of primary mechanism, I think is asphyxia and the secondary — or low oxygen — and the secondary mechanism is this physiologic stress. But ultimately the cause of death is the subdual restraint and compression.”

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Dr. Lindsey Thomas, a forensic pathologist, testified on Friday that police restraint killed George Floyd, primarily by restricting his oxygen with a secondary effect of physiological stress on his body.CreditCredit...Court TV still image, via Associated Press
  • Like several other medical witnesses who testified this week, Dr. Thomas came to the conclusion that Mr. Floyd died from a deprivation of oxygen. This has been a primary argument of the prosecution, which is seeking to dispel the defense’s notion that drug use played a larger role. “There’s no evidence to suggest he would have died that night, except for the interactions with law enforcement,” Dr. Thomas said. Her testimony followed that of two other medical witnesses, who testified on Thursday with the same conclusions. In addition, Dr. Thomas differentiated Mr. Floyd’s death from a sudden cardiac arrest, saying that Mr. Floyd’s oxygen deprivation came more slowly and that “the point is that it’s due to law enforcement’s subdual, restraint and compression.”

April 9, 2021, 5:05 p.m. ET

The police caused George Floyd’s death, but drugs and heart disease played a role, the medical examiner says.

Dr. Andrew Baker, the medical examiner who conducted George Floyd’s autopsy, said the actions of police officers were the primary cause of Mr. Floyd’s death, though other factors played a role.
Credit...Court TV still image, via Associated Press

The medical examiner who conducted George Floyd’s autopsy testified on Friday that while Mr. Floyd’s heart disease and drug use contributed to his death, it was police officers’ compression of his neck and restraint of his body that were the primary causes.

The testimony of Dr. Andrew Baker, who has been the chief medical examiner in Hennepin County since 2004, was perhaps the most important yet for prosecutors who hope to convince jurors that Derek Chauvin killed Mr. Floyd when he knelt on him for more than nine minutes last May. Mr. Chauvin’s lawyer has suggested that Mr. Floyd’s heart disease, or the fentanyl and methamphetamine in his system, might have caused his death.

Dr. Baker testified that Mr. Floyd’s narrowed arteries, hypertension and drug use likely made him more susceptible to dying as a result of being pinned to the ground by three police officers. But, he said, Mr. Floyd’s health and use of drugs were not direct causes.

“In my opinion, the law enforcement subdual, restraint and the neck compression was just more than Mr. Floyd could take, by virtue of those heart conditions,” Dr. Baker said.

Dr. Baker said he believed Mr. Chauvin’s knee had compressed Mr. Floyd’s neck. Mr. Chauvin’s lawyer has suggested that Mr. Chauvin’s knee may have been closer to Mr. Floyd’s shoulder blade or back.

The testimony of medical experts has become crucial in the trial of Mr. Chauvin, who is facing charges including second-degree murder in Mr. Floyd’s death. The prosecution and defense have proposed juror instructions that say Mr. Chauvin should be considered to have caused Mr. Floyd’s death if he was a “substantial causal factor,” even if there were other contributing causes.

Prosecutors have called a series of medical experts to the witness stand over the past two days. They include a lung doctor who testified that even a healthy person would have died under Mr. Chauvin’s knee and a forensic pathologist who had trained Dr. Baker and said that the actions of police were what caused Mr. Floyd’s death. Mr. Chauvin’s lawyer is expected to call his own medical experts after prosecutors rest their case.

Even as Dr. Baker was clear that he found the restraint and compression of Mr. Floyd by police officers to be the main causes of his death, he suggested more strongly than previous experts that Mr. Floyd’s heart disease and drug use put him at greater risk. He said Mr. Floyd had an enlarged heart and “very severe underlying heart disease.”

“He has a heart that already needs more oxygen than a normal heart, by virtue of its size, and it’s limited in its ability to step up to provide more oxygen when there’s demand because of the narrowing of his coronary arteries,” Dr. Baker said.

But, he added later, it was the confrontation between the police and Mr. Floyd that had “tipped him over the edge.”

During Dr. Baker’s testimony, a prosecutor showed autopsy photographs of Mr. Floyd’s body for the second time. Dr. Baker said they showed marks on his wrists that likely came from handcuffs, scrapes on one of his cheeks and on his forehead, a cut on his lip and bruises on his nose that were consistent with being pressed against the street.

The medical examiner said he had intentionally not watched the bystander video of Mr. Floyd’s arrest before he conducted the autopsy because he did not want to have any preconceived notion about what had happened as he examined Mr. Floyd’s body. But he said he had watched the video after the autopsy and had considered it and other video evidence before he determined the cause and manner of death.

April 9, 2021, 4:53 p.m. ET

Reporting from Kansas City

Testimony has ended for the week and will resume on Monday.

April 9, 2021, 4:33 p.m. ET

Dr. Baker agreed with the defense that Floyd’s death was a “multi-factorial process.” He said that Floyd had heart disease and that methamphetamine was “hard on the heart.” But in response to subsequent questions from the prosecution, he said that the drugs and heart disease, while “contributing conditions,” were “not direct causes of Mr. Floyd’s death.”

April 9, 2021, 4:33 p.m. ET

Reporting from Kansas City

Chauvin’s lawyer has finished his cross-examination. He emphasized the basic theme he has been advancing all trial — that George Floyd was in bad health, and that it was drugs and his own resistance that killed him. The challenge for the defense is that they are asking jurors to look at everything that happened to Floyd that day except the thing their client did, which was kneel on Floyd’s neck.

April 9, 2021, 4:22 p.m. ET

The defense asked whether fentanyl could have caused the lung abnormalities found at autopsy. Dr. Baker said it was possible but less likely than other causes. The defense then asked whether the level of fentanyl found in Floyd’s blood could be fatal. “In other circumstances it would be a fatal level,” Dr. Baker said, such as if that had been the only finding and Floyd had been found “home alone in his locked residence with no evidence of trauma.” But, he added, interpreting drug concentrations “is very context dependent.”

April 9, 2021, 4:12 p.m. ET

Reporting from Kansas City

In questioning Dr. Baker, Chauvin’s lawyer is raising the point that there were no bruises or visible injuries found on George Floyd’s neck or back. The lawyer, Eric Nelson, seems to be suggesting that the absence of those injuries might mean that the pressure placed on Floyd was not enough to cause him to die from lack of oxygen. The problem with this is that one expert after the next — including Dr. Baker — has said that people who asphyxiate don’t necessarily have to have bruises.

April 9, 2021, 4:04 p.m. ET

Doctors are trained to know the difference between correlation and causation. For example, someone can die shortly after an intervention — the two events being related in time — but not necessarily because of that intervention. I noticed that when Dr. Baker was asked to define what he meant by death “complicating” the police's actions, he said it was “on the heels of.” He did not himself use the word “caused.”

April 9, 2021, 4:09 p.m. ET

Still, this may not have been necessary, given that the reference to law enforcement’s subdual, restraint and compression of Floyd was listed under the immediate “cause of death” heading on the death certificate.

April 9, 2021, 3:51 p.m. ET

In their own words: The interaction with police ‘was just more than Mr. Floyd could take.’

Dr. Andrew Baker, the medical examiner who performed George Floyd’s autopsy, testified on Friday that Mr. Floyd had severe underlying heart disease, including hypertensive heart disease, but that ultimately the interaction with law enforcement was what caused Dr. Baker to rule his death a homicide:

He has a heart that already needs more oxygen than a normal heart by virtue of its size and it’s limited in its ability to step up to provide more oxygen when there is demand because of the narrowing of his coronary arteries. Now, in the context of an altercation with other people, that involves things like physical restraint, that involves things like being held to the ground, that involves things like the pain that you would incur from having your, you know, your cheek up against the asphalt, an abrasion on your shoulder. Those events are going to cause stress hormones to pour out into your body, specifically things like adrenaline. And what that adrenaline is going to do is it’s going to ask your heart to beat faster. It’s going to ask your body for more oxygen so that you can get through that altercation. And in my opinion, the law enforcement, subdual restraint and the neck compression was just more than Mr. Floyd could take by virtue of those heart conditions.

April 9, 2021, 3:43 p.m. ET

The defense gives Dr. Baker another chance to clarify what he meant by “complicating.” He says, “It means that an intervention occurred and there was an outcome that was untoward on the heels of that intervention.” He uses the analogy of complications that occur in the hospital.

April 9, 2021, 3:43 p.m. ET

Reporting from Kansas City

With this being the heart of the case — the cause of George Floyd’s death — Derek Chauvin’s lawyer, Eric Nelson, has his work cut out for him to shoot down what Dr. Baker said: that Floyd died in part because he was restrained by Chauvin and other officers.

April 9, 2021, 3:32 p.m. ET

It is worth noting that according to the proposed jury instructions, in order for jurors to find Chauvin guilty, his actions need only have been a “substantial causal factor” in Floyd’s death, not the only factor in it.

April 9, 2021, 3:29 p.m. ET

Reporting from Kansas City

The prosecution’s questioning of Dr. Baker was quite concise. But I think we can expect a very thorough — and probably combative — cross-examination, as the defense is likely to bring up past statements in which Dr. Baker might have deviated from what he said in court today.

April 9, 2021, 3:20 p.m. ET

Dr. Baker said that medical examiners are allowed to classify the manner of death as “undetermined” if the circumstances are unclear. In this case, though, he classified George Floyd's death as “homicide.”

April 9, 2021, 3:22 p.m. ET

Finally, Dr. Baker gets to translate a word he used in his description of the cause of death: “complicating,” which led to confusion about his meaning. The full phrase was “cardiopulmonary arrest complicating law enforcement subdual, restraint, and neck compression.” Dr. Baker agreed that in this case, “complicating” meant “in the setting of.”

April 9, 2021, 3:28 p.m. ET

Dr. Baker said that in his opinion, Mr. Floyd’s underlying heart disease meant that his heart needed more oxygen than a normal heart. In the context of physical restraint, he said, with adrenaline surging in Floyd’s body asking his heart to beat faster, “the law enforcement subdual, restraint and the neck compression was just more than Mr. Floyd could take by virtue of those heart conditions.”

April 9, 2021, 3:10 p.m. ET

Reporting from Kansas City

The defense has suggested that George Floyd swallowed a meth and fentanyl pill when the officers approached him. Dr. Baker, the medical examiner who performed the autopsy on Floyd, said he did not find any pill fragments in his stomach.

April 9, 2021, 3:08 p.m. ET

Dr. Baker described George Floyd’s lungs as “edematous,” meaning fluid-filled. He said this was a non-specific finding — it has multiple potential causes, including the CPR that Floyd received. It's possible that the defense will ask whether it might have been a rare complication of fentanyl use known as flash pulmonary edema.

April 9, 2021, 3:12 p.m. ET

This is more often associated with the administration of drugs — such as naloxone, known as Narcan — to reverse the effects of opioids.

April 9, 2021, 3:00 p.m. ET

The prosecution is having Dr. Baker walk through how an autopsy is done, including documenting the injuries found on the skin of George Floyd’s face. Dr. Baker agreed that these were consistent with his being pinned against the pavement.

April 9, 2021, 2:58 p.m. ET

Reporting from Minneapolis

To us watching, it has seemed like the prosecution was trying to diminish the importance of Dr. Baker, the medical examiner, as a witness. But I wonder if the jury is thinking, finally the opening acts are over and the headliner is here.

April 9, 2021, 2:57 p.m. ET

How the medical examiner’s previous statements may help the defense.

On Friday afternoon, the prosecution called the Hennepin County medical examiner, Dr. Andrew Baker, to the stand. The state may want to keep his testimony as short as possible, in part because of indications that he made several statements that could hurt their case, and that could come up while he is on the stand. Here’s what they are:

  • That Mr. Floyd’s blood had what would have been “a fatal level of fentanyl under normal circumstances,” according to notes from a video meeting with prosecutors on May 31.

  • That “if he were found dead at home alone and no other apparent cause, this could be acceptable to call an overdose,” according to notes from a June 1 interview by investigators. The notes say that Dr. Baker added, “I am not saying this killed him.”

  • That untreated hypertension would increase the risk of death, meaning the subject would “get to death quicker” because of an increased need for oxygen, according to notes taken during that interview. “Certain intoxicants” could exacerbate the problem, the notes say.

  • That nothing that occurred when Mr. Floyd was on the ground was a factor in Mr. Floyd’s death, according to a summary of a July 8 F.B.I. interview relayed in a conversation between the U.S. Attorney’s Office and the Hennepin County Attorney’s Office. A letter from the county disputed that summation, saying that the “subdual, restraint and neck compression” cited by Dr. Baker as the cause of death “included the time that Mr. Floyd was on the ground.”

  • That “a prone position is not in and of itself more dangerous than other positions” according to the medical literature. This most likely refers to studies that the prosecution has taken pains to discredit. The state’s expert witnesses have said that the studies do not reflect real-world conditions.

April 9, 2021, 2:34 p.m. ET

Next up is Dr. Andrew Baker, the medical examiner for Hennepin County, who performed George Floyd’s autopsy.

April 9, 2021, 2:38 p.m. ET

Dr. Baker says he chose not to watch the videos of George Floyd’s death until after examining his body at autopsy.

April 9, 2021, 2:40 p.m. ET

This points to why forensic pathologists say it can be dangerous to release preliminary findings from a medical examiner, because not all of the relevant evidence has yet been taken into account.

April 9, 2021, 2:41 p.m. ET

“The autopsy is just one piece of the medical examiner’s death investigation,” Dr. Baker says.

April 9, 2021, 2:33 p.m. ET

Dr. Andrew Baker, Hennepin County’s chief medical examiner, takes the stand.

Dr. Andrew Baker, the Hennepin County medical examiner, testified on Friday at former officer Derek Chauvin’s trial that he found bruises on George Floyd’s body during the initial autopsy.

Dr. Baker, who determined during his autopsy that Mr. Floyd died from “cardiopulmonary arrest” and declared his death a homicide, was reappointed as chief medical examiner by the Hennepin County Board of commissioners in June for a fifth term, just a month after Mr. Floyd’s death.

The medical examiner’s office is responsible for examining all unexpected deaths in the counties of Hennepin, Scott and Drake, according to its website.

Dr. Baker graduated from University of Iowa medical school in 1992, and did his residency in pathology at the school’s hospital system. He became an active duty medical officer in the Air Force in 1998, where his work took him to Kosovo and the site of the U.S.S. Cole bombing.

He has said that his most memorable work experience was working on the autopsy of victims of the plane that crashed into the Pentagon on 9/11. He also did pro bono work for the Innocence Project.

The autopsy is one piece of the medical examiner’s death investigation, Dr. Baker said. Other things taken into account include medical history, circumstances surrounding the person’s death and more to determine the cause and manner of death.

In court, Dr. Baker said he “intentionally chose” not to view the video of Mr. Floyd’s death until after he performed the autopsy.

While examining photos he took of Mr. Floyd during the autopsy, Dr. Baker said he observed injuries on Mr. Floyd’s face — bruising and scrapes on left side of his forehead and left side of his cheek. There was also an abrasion on his left shoulder, he said, consistent with lying in the prone position on sidewalk, and blunt force injuries on knuckles on the back of his right hand.

Dr. Baker told the jury he did not take a photograph of Mr. Floyd’s heart intact because he did not usually “photograph organs that appear to be perfectly normal,” he said.

The arteries in Mr. Floyd’s heart were significantly narrowed and his heart was enlarged based on its weight, he said.

Dr. Baker also examined the contents of Mr. Floyd’s stomach during the autopsy, and said he did not find evidence of pills, but noted that he did not have the content tested in a lab. He also found a tumor in Mr. Floyd’s abdomen, but said he had no reason to believe it contributed to his death.

April 9, 2021, 1:36 p.m. ET

Police officers, not drugs, caused George Floyd’s death, a pathologist testifies.

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Forensic Pathologist Testifies That Police Actions Caused Floyd’s Death

Dr. Lindsey Thomas, a forensic pathologist, testified on Friday in Derek Chauvin’s murder trial that George Floyd died from low oxygen caused by law enforcement’s subdual restraint and compression to the neck.

“Well, I was asked to review a lot of the materials and come to an independent conclusion about what I thought the cause, and manner of death were and the mechanism for that cause. I’ve never had a case like this that had such thorough documentation of the terminal events?” “And by way of the thorough documentation, what makes it so thorough, in your opinion?” “Well, the use of videos is unique in this case. Certainly as medical examiners we use videos, but there’s never been a case that I’ve been involved with that had videos over such a long time frame, and from so many different perspectives.” “Do you agree with Dr. Baker’s determination on the cause of death?” “Yes, I do.” “And is that by the word ‘immediate’ on here?” “Yes, cardiopulmonary arrest complicating law enforcement’s subdual restraint and neck compression.” “Have you, Dr. Thomas, formed an opinion about the mechanism of death?” “Yes.” “Would you tell us what that is?” “In this case, I believe the primary mechanism of death is asphyxia or low oxygen. So, this is not a sudden cardiac death, a sudden cardiac arrhythmia. This is a death where both the heart and lungs stopped working. And the point is that it’s due to law enforcement’s subdual restraint and compression. It basically is Mr. Floyd was in a position because of the subdual restraint and compression, where he was unable to get enough oxygen in to maintain his body functions.”

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Dr. Lindsey Thomas, a forensic pathologist, testified on Friday in Derek Chauvin’s murder trial that George Floyd died from low oxygen caused by law enforcement’s subdual restraint and compression to the neck.CreditCredit...Still image, via Court TV

A forensic pathologist testified on Friday that George Floyd had primarily died of low oxygen, also called asphyxia, which she said had been caused by Derek Chauvin and the other police officers who pressed him to the ground.

The testimony from Dr. Lindsey C. Thomas further supported prosecutors’ arguments that Mr. Chauvin, the former Minneapolis police officer who is on trial for murder, killed Mr. Floyd by kneeling on him for more than nine minutes.

Exactly what caused Mr. Floyd’s death last May has become a central issue in the second week of the trial; Mr. Chauvin’s lawyer has suggested that Mr. Floyd could have died from a heart condition or the fentanyl and methamphetamine that were found in his system.

Dr. Thomas has worked in several medical examiner’s offices over 36 years and said she had performed at least 5,000 autopsies. She also helped to train Dr. Andrew Baker, the current Hennepin County medical examiner who performed the autopsy on Mr. Floyd and who was also scheduled to testify on Friday.

She said she agreed with Dr. Baker’s finding that Mr. Floyd’s death was a homicide and that the cause was “cardiopulmonary arrest complicating law enforcement’s subdual restraint and neck compression.”

That phrase had caused some confusion in the months after it was issued, and Mr. Chauvin’s lawyer, Eric J. Nelson, asked Dr. Thomas on Friday if “complicating” could mean different things to different experts; she agreed. But Dr. Thomas said that in this case, she found it to mean that Mr. Floyd’s heart had stopped because of the police officers’ actions.

“Mr. Floyd was in a position, because of the subdual, restraint and compression, where he was unable to get enough oxygen in to maintain his body functions,” Dr. Thomas testified.

She said that physiological stress could be considered a secondary mechanism of Mr. Floyd’s death, after the primary mechanism of asphyxia, but that both were caused by the police officers who pinned Mr. Floyd to the ground.

Dr. Thomas’s testimony came the day after a lung doctor also said that Mr. Floyd had died of a lack of oxygen caused by Mr. Chauvin’s pressure on his neck and back. Mr. Nelson is expected to call his own experts later in the trial after prosecutors rest their case. Dr. Thomas, like other experts called by prosecutors, rebutted the defense’s argument that drugs could have caused Mr. Floyd’s death.

“There’s no evidence to suggest he would have died that night, except for the interactions with law enforcement,” Dr. Thomas said.

During her testimony, a prosecutor provided autopsy photographs of Mr. Floyd’s body, hands, shoulders and face to jurors, but they were not shown publicly. Dr. Thomas used the photographs to show and describe scrapes on Mr. Floyd’s hands that she said had come from the handcuffs.

In his cross-examination, Mr. Nelson asked her several questions about Mr. Floyd’s heart, which was larger than average, and also asked her about hypothetical situations.

“You find a person at home, no struggle with the police, the person doesn’t have a heart problem,” Mr. Nelson said, laying out a hypothetical situation. “If you find fentanyl and methamphetamine in this person’s system at the levels that they are at, would you certify this as an overdose?”

Dr. Thomas responded: “Again, in the absence of these other realities, yes, I could consider that to be an overdose.”

But Dr. Thomas said the autopsy had ruled out various other causes of death, including a heart attack, and that Dr. Baker’s labeling of the death as a homicide had ruled out an overdose on drugs, which would almost always be described as an accident. Nothing in an autopsy alone would prove that Mr. Floyd had died of low oxygen, she said; for that reason, she said, the videos of Mr. Floyd’s death were vital to her analysis.

In another exchange, Mr. Nelson asked Dr. Thomas about a study in Canada that analyzed about 3,000 situations in which a suspect was placed in a prone position by police. Mr. Nelson asked Dr. Thomas if she was aware that no one in that study had died.

“Isn’t that amazing?” Dr. Thomas responded. “When you consider that virtually every forensic pathologist in the United States has probably had an officer-involved death like this, how did they — it utterly baffles me — which is why I kept saying ‘Canada,’ because I don’t know what’s different, but —”

At that point, Mr. Nelson objected and Dr. Thomas was cut off.

April 9, 2021, 1:20 p.m. ET

Reporting from Kansas City

Dr. Thomas has completed her testimony, and the court is now on lunch break until 1:30 Central time.

April 9, 2021, 1:17 p.m. ET

Here’s what we know about the key medical terminology used in the trial.

Dr. Andrew Baker may be one of the most important witnesses to be called in the murder trial of Derek Chauvin. It was his duty to determine why George Floyd died.

Dr. Baker, the Hennepin County medical examiner who is expected to be called to testify on Friday, conducted Mr. Floyd’s initial autopsy and determined ultimately that his heart and lungs stopped functioning while he was being subdued, restrained and compressed by police officers.

The manner of Mr. Floyd’s death, Dr. Baker concluded, was homicide. And in the months since, almost everything he said in the autopsy report has been parsed and pored over by experts and laypeople alike.

We talked with several forensic pathologists uninvolved in the case to explain some of the terms used in the proceedings, how they determine the cause and manner of death and how this relates to the case.

April 9, 2021, 1:09 p.m. ET

Reporting from Kansas City

The prosecution has to prove the case beyond a reasonable doubt, and the defense has to create some doubt in the jurors’ minds. It seems like Derek Chauvin’s lawyer is trying to raise all these other possibilities that could have caused George Floyd’s death, perhaps hoping jurors will feel uncertain that it was indeed Chauvin’s restraint of Floyd that caused his death.

April 9, 2021, 12:41 p.m. ET

Reporting from Kansas City

In her direct testimony, Dr. Thomas said that but for the interaction with the police last May 25, George Floyd would have lived that day. In his cross-examination, Eric Nelson, the defense lawyer, seems to be trying to establish that Floyd’s heart was in such bad shape that he was particularly susceptible to death because of his exertion and drug use before the officers held him down.

April 9, 2021, 12:28 p.m. ET

Reporting from Minneapolis

She may not have an Irish accent, but like Dr. Tobin yesterday, Dr. Thomas is good at explaining things to the jury.

April 9, 2021, 12:24 p.m. ET

Reporting from Minneapolis

I wonder how much confusion, time and effort would have been saved if Dr. Baker had simply put “law enforcement subdual, restraint, and neck compression” as the cause of death, instead of “cardiopulmonary arrest complicating law enforcement subdual, restraint, and neck compression.” Dr. Thomas has testified that it would have meant the same thing.

April 9, 2021, 12:24 p.m. ET

The defense lawyer asked Dr. Thomas to parse perhaps the most confusing aspect of the cause of death the medical examiner listed: the word “complicating” in the phrase “cardiopulmonary arrest complicating law enforcement subdual, restraint, and neck compression.” Dr. Thomas looked down, paused a moment and said, “I guess it could be used in lots of different ways.”

April 9, 2021, 12:28 p.m. ET

She added that in her opinion, it meant that the cardiopulmonary arrest — the ceasing of heart and lung function — was due to the subdual, restraint and compression by law enforcement.

April 9, 2021, 12:17 p.m. ET

The prosecution asked Dr. Thomas about research that concludes that prone restraint is not dangerous. She said the research “bears no resemblance to what Mr. Floyd experienced” because the people in the study were young and healthy and knew the restraint would stop if they were in trouble. The studies were also conducted on the equivalent of a gymnastics mat, she said, “completely different” from hard ground.

April 9, 2021, 12:18 p.m. ET

Reporting from Minneapolis

These studies she is critiquing purport to prove that weight on someone’s back when they are in the prone position does not deplete oxygen to a fatal level. They are often used to defend the police. Dr. Martin J. Tobin, a medical expert who testified yesterday, also criticized the studies, saying they do not replicate real-world conditions.

April 9, 2021, 12:17 p.m. ET

Reporting from Kansas City

And again, it’s all back to the video. Dr. Thomas ends her direct testimony by saying, “From watching the video, I certainly wouldn’t want to be in that position.”

April 9, 2021, 12:11 p.m. ET

Reporting from Minneapolis

We're back from a short morning break. Dr. Thomas says Dr. Baker’s determination that Floyd’s death was a homicide by definition rules out a drug overdose — which is usually classified as an accidental death or, if intentional, a suicide.

April 9, 2021, 12:01 p.m. ET

Reporting from Kansas City

Per a reporter in the courtroom, for the first time since the trial began, there is someone in the seat reserved for a family member of Derek Chauvin. Thus far, a member of George Floyd’s family has been in the courtroom each day.

April 9, 2021, 12:04 p.m. ET

Reporting from Minneapolis

Reporters in the courtroom also note that one of the jurors was questioned by the judge this morning about any inappropriate contacts. The juror said that she had turned on a television and seen coverage of the trial but had quickly turned it off, and that she had not responded to a relative who texted her one day and said it looked like a “bad day” in court. The judge found that she had not acted inappropriately.

April 9, 2021, 11:49 a.m. ET

Reporting from Minneapolis

The court is taking a short morning break. Dr. Lindsey Thomas, a pathologist called by the prosecution to discuss the cause of George Floyd’s death, will resume her testimony at 11:15 a.m. Central time.

April 9, 2021, 11:45 a.m. ET

Dr. Thomas is explaining that a medical examiner’s determination of the manner of death — in this case homicide — is distinct from the determination of a cause of death. Manner of death is generally one of five choices: natural, accident, suicide, homicide or undetermined. Homicide, in the medical context, refers to a death at the hands of another person or other people. It is not a criminal determination — that is up to the courts, as in this case.

April 9, 2021, 11:51 a.m. ET

Immediately following that, there was a discussion of whether a particular exhibit could confuse the jury between the medical definition of homicide and the legal definition.

April 9, 2021, 11:39 a.m. ET

In their own words: ‘There’s no evidence to suggest he would have died that night except for the interactions with law enforcement.’

Dr. Lindsey Thomas, a forensic pathologist who also trained the medical examiner who performed the autopsy on Mr. Floyd, testified that Mr. Floyd did not die of a fentanyl overdose or a pre-existing heart condition, as the defense has indicated.

As a forensic pathologist, I know from hundreds of families describing what happened at the time of death that this death does not fit what has been described in someone who dies of a cardiac arrhythmia from arteriosclerotic heart disease and likewise hypertensive heart disease. Those tend to be cardiac arrhythmias, sudden cardiac deaths. This is not that kind of death. Likewise, fentanyl intoxication, as I described — and again, I don’t treat patients. I don’t see living people — but what I know from family members who describe deaths that then later turn out to be due to fentanyl, the death is slow, it’s peaceful. They fall asleep. They may hear snoring or very heavy breathing. There’s no struggle. They just often are found, just kind of slumped over. It’s a very slow death.

Dr. Thomas also said that police actions during Mr. Floyd’s arrest led to his death:

There’s no evidence to suggest he would have died that night except for the interactions with law enforcement.

April 9, 2021, 11:34 a.m. ET

Now Dr. Thomas is discussing something new, another secondary mechanism of death that she refers to as “physiological stress” — the kind you feel if you’re about to be in a car crash. But instead of fearing for your life for a second, she said, in this case it went on for more than nine minutes.

April 9, 2021, 11:38 a.m. ET

Reporting from Minneapolis

This is key because the defense has referred to the “adrenaline flowing through his body” as a contributor to his death. But Dr. Thomas is attributing the adrenaline to his situation, not to "excited delirium" or other theories the defense might advance.

April 9, 2021, 11:38 a.m. ET

She says the reason this is relevant is that the physiological stress increased the demand on Mr. Floyd’s heart, lungs and muscles, which were already stressed by his restraint. “It’s kind of a double whammy to his heart and lungs” and whole system.

April 9, 2021, 11:25 a.m. ET

Reporting from Minneapolis

Dr. Thomas is explaining what she sees in autopsy photos of Floyd. The photos are being shown to the jury and spectators in the court, but not publicly — presumably because the judge thinks they are too gruesome to show on television.

April 9, 2021, 11:30 a.m. ET

Reporting from Minneapolis

I believe this is the first time I have seen them physically hand out the exhibits rather than displaying them on the screen.

April 9, 2021, 11:17 a.m. ET

Dr. Thomas, commenting on the fact that the word "asphyxia" does not appear on the death certificate, said she likewise avoids using that word because it requires too much explanation. One medical examiner I interviewed said that forensic pathologists refine the way they report their findings over the course of their careers to ensure that the public and people in the legal system, who may be reading what they write, better understand it.

April 9, 2021, 11:11 a.m. ET

George Floyd’s death certificate mentions “other contributing conditions” including heart disease and the presence of fentanyl and methamphetamine. Dr. Thomas explained that medical examiners document contributing factors mainly to help public health experts track deaths across a population. She said these were not the cause of death in Floyd’s case.

April 9, 2021, 11:09 a.m. ET

In their own words: ‘This is a death where both the heart and lungs stopped working.’

Dr. Lindsey Thomas, the forensic pathologist who helped train Dr. Andrew Baker, the Hennepin County Medical Examiner who performed an autopsy on George Floyd, testified on Friday. Dr. Thomas said Mr. Floyd died of low oxygen caused by the arresting officers’ restraint and compression at the time of arrest:

Well, it’s kind of in two parts. So there’s the cardiopulmonary arrest, which doesn’t provide a lot of additional clarifying information because in a way, everyone dies of when your heart stops and your lungs stop — that’s cardiopulmonary arrest. But as a forensic pathologist, I would use cardiopulmonary arrest to differentiate it from a cardiac arrest. So this is not a sudden cardiac death, a sudden cardiac arrhythmia. This is a death where both the heart and lungs stopped working and the point is that it’s due to law enforcement’s subdural restraint and compression. That is kind of what ultimately is the immediate cause of death, is the subdural restraint and compression.

April 9, 2021, 10:57 a.m. ET

Dr. Thomas said that George Floyd died because “he was not able to get enough oxygen in to maintain his bodily functions.” She said she came to that conclusion mainly from “evidence from the terminal events, the video evidence that show Mr. Floyd in a position where he was unable to adequately breathe.”

April 9, 2021, 10:53 a.m. ET

Reporting from Minneapolis

The question is, why did the prosecution want Dr. Thomas to explain the death certificate Dr. Baker issued? Did they think that he would not explain it as simply? Big questions about what he will say when he takes the stand today.

April 9, 2021, 10:57 a.m. ET

Reporting from Kansas City

I know some have criticized prosecutors for calling too many experts. But I wonder if there is a cumulative effect of having so many testify that prosecutors hope will outweigh the defense experts. If the person who trained the medical examiner says George Floyd’s death was caused by the police, that seems to be a big deal.

April 9, 2021, 10:51 a.m. ET

Reporting from Kansas City

Dr. Thomas is reinforcing not only the prosecution’s theory about the cause of death, but also the point that prosecutors have tried to get jurors to pay attention to — the video! Dr. Thomas said she needed to watch the video to really determine what led to George Floyd’s death.

April 9, 2021, 10:52 a.m. ET

Reporting from Kansas City

As a reminder, the defense has said the case is about more than the video. The prosecution has said that it’s all in the video.

April 9, 2021, 10:56 a.m. ET

Reporting from Minneapolis

Medical examiners will always tell you that they cannot tell everything from simply examining the body. They need to know the circumstances of the death. In this case, the video is medically relevant information — without it, Dr. Thomas is saying, you might not be able to determine how he died.

April 9, 2021, 10:50 a.m. ET

Reporting from Minneapolis

The state is also trying to push back on the defense’s argument that Dr. Baker’s findings help Chauvin because he didn’t cite asphyxia. Dr. Thomas is essentially saying that Dr. Baker’s report was just a starting point, and that ultimately asphyxia was the mechanism of death.

April 9, 2021, 10:50 a.m. ET

Reporting from Minneapolis

Finally someone is breaking down the awkward syntax (at least to the lay person) of the autopsy cause of death: “What it means to me is that the activities of the law enforcement officers resulted in Mr. Floyd’s death.”

April 9, 2021, 10:48 a.m. ET

Reporting from Kansas City

“The point is that it’s due to law enforcement subdual restraint and compression.” That’s a big statement from Dr. Thomas, basically saying Floyd's death was caused by the police.

April 9, 2021, 10:49 a.m. ET

Dr. Thomas clarified words in the medical examiner's report that have confused many people. She said that “cardiopulmonary arrest” does not mean a heart attack.

April 9, 2021, 10:44 a.m. ET

How the prosecution tried to pre-empt potential problems for them in the medical examiner’s testimony.

A defense lawyer, Eric Nelson, questioning a witness on Thursday.
Credit...Court TV still image, via Associated Press

On Friday the prosecution will present a key witness, but one who is potentially damaging to its case: the Hennepin County medical examiner, Dr. Andrew Baker.

Dr. Baker, a prominent figure in the forensic pathology community, found that George Floyd’s death was a homicide caused by “law enforcement subdual, restraint, and neck compression.”

On its face, that conclusion would seem to work very much in the prosecution’s favor. But Dr. Baker did not mention asphyxia, or deprivation of oxygen, in the autopsy.

According to a summary of “preliminary findings” written by county prosecutors before the state attorney general took over the case, “the autopsy revealed no physical findings that support a diagnosis of traumatic asphyxia or strangulation” — a summary that the defense may use to guide its questioning even though Dr. Baker did not include it in his final report.

Two forensic pathologists hired by the Floyd family, Dr. Michael Baden and Dr. Allecia Wilson, said asphyxia was the cause of death, and the prosecution is making the same assertion.

The state’s lawyers have taken the unusual step of distancing themselves from Dr. Baker. They did not use him as their lead medical witness — that was Dr. Martin Tobin, a pulmonologist who has written several books about the lungs and breathing. And in opening statements, Jerry Blackwell, a prosecutor, said that “cardiopulmonary arrest,” listed by Dr. Baker in the cause of death section of the death certificate, just means death. The defense lawyer, Eric J. Nelson, made the most of this, saying in his opening statement, “The state was not satisfied with Dr. Baker’s work.”

On Thursday, Dr. Tobin and another expert witness, Dr. William Smock, the police surgeon for the Louisville Metro Police Department, both cited oxygen deprivation as the cause of death for Mr. Floyd. Both said evidence of that would not have shown up on the autopsy report.

Dr. Tobin said he would not expect to find injury to the hypopharynx, a narrow section of the airway which he said had been compressed by the pressure on Mr. Floyd’s neck and the reduction of volume in his lungs. The absence of bruising on the neck from Derek Chauvin’s knee, he said, was not significant.

“Whenever I go to church, I sit on a hard bench. I don’t get bruising of my buttocks when I leave,” he said. “This was a static force, it’s not as if somebody is jamming against it. So you wouldn’t expect anything in the way bruising.”

Asked about low-oxygen deaths, Dr. Tobin said he would not expect them to leave a “fingerprint” on the autopsy.

“Does it mean that the person didn’t die from low oxygen?” the prosecutor, Mr. Blackwell, pressed him.

“No, absolutely not,” he said. “So if you take somebody and you suffocate them with a pillow and it’s very clear to you, after you suffocated the person and he’s dead from the pillow, you’re not going to see the effects of the low oxygen.”

Similarly, Dr. Smock said he teaches students that strangulation may not show up on autopsies. “You can have someone put your biceps and forearm on either side of your neck and squeeze, render you unconscious, even kill you,” he said. “And you will never, ever see a bruise on the neck. And the reason is you’re applying a broad surface area, biceps and forearm, to a broad surface area.”

The first witness on Friday, Dr. Lindsey C. Thomas, a forensic pathologist who helped train Dr. Baker, was expected to underscore this point and explain that in over half of cases when people die of insufficient oxygen, the body tissues may show no signs of it.

April 9, 2021, 10:39 a.m. ET

The prosecution is having Dr. Thomas describe the role of a medical examiner and also the limitations of that person's expertise — for example, she agreed that measuring lung volumes or air reserves in a living person would not be in a forensic pathologist's bailiwick. It's possible that the prosecution is doing this to put into context what the jurors will hear later from the actual medical examiner in this case.

April 9, 2021, 10:42 a.m. ET

Reporting from Minneapolis

I think that’s exactly why the state called her. She is essentially saying that determining cause of death involves more than just the physical examination of the body, which is what the local medical examiner, Dr. Andrew Baker, did in performing the autopsy. Notably, Dr. Baker did not cite asphyxia, and that has worried the prosecution.

April 9, 2021, 10:46 a.m. ET

Reporting from Minneapolis

Dr. Thomas said that she was involved in training Dr. Baker, the medical examiner, and that she is a friend of his. The state is trying to bolster Dr. Baker’s credibility while at the same time making the case that his autopsy findings — which did not cite asphyxia, which the state has said was the cause of Floyd’s death — do not preclude asphyxia.

April 9, 2021, 10:47 a.m. ET

Dr. Thomas said she agreed with the medical examiner’s conclusion as to cause of death. She added that she believed the primary mechanism of death — which is distinct from the cause — was “asphyxia or low oxygen.”

April 9, 2021, 10:23 a.m. ET

Dr. Lindsey Thomas, forensic pathologist, takes the stand.

Dr. Lindsey C. Thomas, a forensic pathologist, took the stand on Friday morning.
Credit...Still image, via Court TV

The state called Dr. Lindsey Thomas, a forensic pathologist, to the stand on Friday morning to testify as an expert witness in the trial of Derek Chauvin.

Dr. Thomas helped train Dr. Andrew Baker, the Hennepin County Medical Examiner who performed an autopsy on George Floyd, and was expected to speak about his findings.

She has more than 36 years of experience working in medical examiner’s offices. She now works as a consulting forensic pathologist and part time in medical examiners officers in Reno, Nev. and Salt Lake City, Utah. Dr. Thomas previously served as assistant medical examiner at the Hennepin County Medical Examiner’s Office and the chief of the Minnesota Regional Medical Examiner’s Office.

She is licensed in Minnesota, Wisconsin, Tennessee, Nevada and Utah.

Dr. Thomas said Dr. Baker was a pathology resident when she was on staff at Hennepin County and she played a role in his training.

She has testified in court before, as a medical examiner and as an expert witness consultant :Dr. Thomas is not being paid for her testimony, she said.

“I knew this was going to be important and I felt like I had something to offer and I wanted to do what I could to help explain what I think happened,” she said.

In court, Dr. Thomas said she has performed more than 5,000 death investigations, which entail analyzing a deceased person’s past medical history, social history, family history, what happened around the time of their death, and a physical examination of the body.

Ahead of appearing in court, she said she reviewed materials from the Hennepin County Medical Examiner, including the toxicology report, photographs, Mr. Floyd’s past medical records, bystander, surveillance and body camera videos.

“I’ve never had a case like this that had such thorough documentation of the terminal event,” she said.

Dr. Thomas said she agreed with Dr. Baker’s finding that the cause of death was “cardiopulmonary arrest complicating law enforcement’s subdual restraint and neck compression.”

That means, she said, that the “activities that the law enforcement officers resulted in Mr. Floyd’s death, specifically those activities were the surgical overstrained and neck compression.”

She added that the mechanism of Mr. Floyd’s death was “asphyxia or low oxygen,” a conclusion she said she reached primarily through review of video footage of Mr. Floyd’s final minutes. The autopsy, she said, was helpful for ruling things out, including a heart attack.

April 9, 2021, 9:05 a.m. ET

The medical examiner who performed the initial autopsy of George Floyd is set to testify.

Dr. Andrew Baker, the Hennepin County medical examiner, determined that George Floyd died from “cardiopulmonary arrest.”
Credit...Richard Sennott/Star Tribune, via Alamy

The Hennepin County medical examiner who performed the initial autopsy of George Floyd is expected to testify in Derek Chauvin’s trial on Friday, a prosecutor said, along with other medical expert witnesses who will discuss Mr. Floyd’s cause of death.

The medical examiner, Dr. Andrew Baker, determined during his autopsy that Mr. Floyd died from “cardiopulmonary arrest” and declared his death a homicide.

The prosecution has signified that it believes that Dr. Baker’s diagnosis was vague; through the testimony of other medical witnesses, it has tried to convince jurors that Mr. Floyd died from asphyxia, or a deprivation of oxygen.

The witnesses on Friday will come on the heels of weighty testimony. On Thursday, two witnesses said a thorough review of video evidence gave no indication that Mr. Floyd died of an overdose. Instead, they concluded that he died from insufficient oxygen.

The defense of Mr. Chauvin, the former Minneapolis police officer charged with murdering Mr. Floyd, has sought to pin the cause of death on Mr. Floyd’s drug use and a heart condition. A toxicology report found fentanyl and methamphetamine in Mr. Floyd’s system, and pills recovered at the scene contained both of the same drugs.

But the argument that Mr. Floyd died from an overdose was rejected by Dr. Bill Smock, the surgeon for the Louisville Metropolitan Police Department, who said that Mr. Floyd’s behavior in the minutes before his death did not match those of the typical person who overdoses on fentanyl.

While pinned to the ground by Mr. Chauvin, Mr. Floyd appeared alert and aware, begging for breath and crying out to “Mama.” In a typical opioid overdose, Dr. Smock said, people slip out of consciousness without a fight. “That is not a fentanyl overdose,” he said. “That is somebody begging to breathe.”

Similarly, Dr. Martin J. Tobin, a pulmonologist and critical care physician from the Chicago area, said Mr. Floyd died from a lack of oxygen while Mr. Chauvin pinned him to the pavement for nine and a half minutes. “A healthy person subjected to what Mr. Floyd was subjected to would have died,” he said.

Dr. Tobin ran through the arrest in vivid detail, pinpointing what he believed to be key moments, including when Mr. Chauvin lifted his feet off the ground, further shifting his body weight onto Mr. Floyd, and the exact moment Mr. Floyd took his last breath.

“You can see his eyes — he’s conscious — and then you see that he isn’t,” Dr. Tobin said as he watched a bystander video of the arrest. “That’s the moment the life goes out of his body.”

April 9, 2021, 7:47 a.m. ET

‘One second he’s alive, and one second he’s no longer,’ a pulmonologist testifies.

Dr. Martin Tobin answering questions during the ninth day of the trial of the former Minneapolis police officer Derek Chauvin.
Credit...Court TV still image, via REUTERS

It was a video everyone in the courtroom has been shown repeatedly, of George Floyd facedown on the street with Derek Chauvin’s knee on his neck. But this time, it was slowed down so the jury could see the briefest widening of Mr. Floyd’s eyes — what the expert witness on the stand on Thursday said was his last conscious moment.

“One second he’s alive, and one second he’s no longer,” said the witness, Dr. Martin Tobin, adding, “That’s the moment the life goes out of his body.”

Dr. Tobin, a pulmonologist who specializes in the mechanics of breathing, presented the prosecution’s first extended testimony on a central question in the murder trial of Mr. Chauvin: how George Floyd died. “You’re seeing here fatal injury to the brain from a lack of oxygen,” Dr. Tobin said.

Dr. Tobin said that Mr. Chauvin and other police officers had restricted Mr. Floyd’s breathing by flattening his rib cage against the pavement and pushing his cuffed hands into his torso, and by the placement of Mr. Chauvin’s knees on his neck and back.

Leaning into the microphone, tie slightly askew, Dr. Tobin used his hands and elbows to demonstrate how people breathe. He gave anatomy lessons by asking jurors to palpate their own necks, and showed an artist’s rendering of how three officers, including Mr. Chauvin, had been positioned on Mr. Floyd.

Dr. Tobin said he had watched portions of the video evidence hundreds of times. He had calculated what he said was the exact amount of weight Mr. Chauvin had placed on Mr. Floyd’s neck (86.9 pounds), clocked Mr. Floyd’s respiratory rate and marked the instant he took his final breath: 8:25:15 p.m.

April 8, 2021, 7:00 p.m. ET

A look at the security surrounding the courthouse.

Security is tight around the Hennepin County Government Center, where the trial is taking place.