Key Moments on Day 10 of the Derek Chauvin Trial

George Floyd’s struggle to breathe while under Mr. Chauvin’s knee has become a major discussion during testimony.

A livestream of Dr. Bill Smock, a police surgeon, testifying in the Derek Chauvin trial this week.
Credit...Stephen Maturen/Getty Images

The trial of the former officer Derek Chauvin will end its second week on Friday after testimony from several witnesses about George Floyd’s precise cause of death. Mr. Floyd was pinned to the ground for more than nine minutes by Mr. Chauvin’s knee; prosecutors are arguing that he died from asphyxia, while the defense says that drugs in his system may be the cause.

Here are some key takeaways from recent testimony.

One of the most anticipated witnesses, the Hennepin County medical examiner who performed the initial autopsy of Mr. Floyd, testified 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.

Though multiple contributing factors may have contributed to Mr. Floyd’s death, Dr. Baker said he believed 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.

Mr. Floyd had an enlarged heart for his size, 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.

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.

A forensic pathologist testified on Friday that Mr. Floyd had primarily died of low oxygen, also called asphyxia, which she said had been caused by Mr. 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.

“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, 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.

A veteran lung doctor testified on Thursday that George Floyd’s death was caused in part by Derek Chauvin’s knees pressing against his neck and back, making it impossible for him to breathe, and that Mr. Floyd showed signs of a brain injury about four minutes before Mr. Chauvin lifted his knee from his neck.

Dr. Martin J. Tobin, a pulmonologist and critical care doctor in Chicago, said in court that the combination of Mr. Chauvin’s pressure, the handcuffs pulling Mr. Floyd’s hands behind his back and Mr. Floyd’s body being pressed against the street had caused him to die “from a low level of oxygen.”

After analyzing videos of the arrest, Dr. Tobin said he determined that Mr. Chauvin had pressed his left knee on Mr. Floyd’s neck for more than 90 percent of the time that Mr. Floyd was on the ground, and that he had kept his right knee on Mr. Floyd’s back for a majority of the time as well. That pressure, combined with having his hands cuffed behind his back and pushed into the street facedown, had cut off oxygen and caused his heart to stop, Dr. Tobin said.

Dr. Tobin outlined four factors that he said had caused Mr. Floyd to lose oxygen and die: The left knee of Mr. Chauvin on Mr. Floyd’s neck, Mr. Chauvin’s right knee on Mr. Floyd’s back and side, Mr. Floyd being handcuffed as he was lying in the street, and Mr. Floyd being held in the prone position. These factors had combined to only allow Mr. Floyd to take small breaths, which were not enough to bring air to the parts of the lungs that allow oxygen to get into blood.

“A healthy person subjected to what Mr. Floyd was subjected to would have died,” Dr. Tobin said.

Fentanyl and methamphetamine were found in Mr. Floyd’s system, and the possibility that they caused his death is a crucial argument for Mr. Chauvin’s defense as the trial enters a phase in which medical testimony is front and center.

Mr. Chauvin’s lawyer, Mr. Nelson suggested on Thursday that Mr. Floyd could have died of a fentanyl overdose if he had taken the drug in the moments before police officers pushed him to the ground. Dr. Tobin said that, unlike someone who died of a fentanyl overdose, Mr. Floyd had never gone into a coma. Mr. Nelson also sought to portray the medical care that Mr. Floyd received from paramedics as lacking; it took them nine minutes to insert a tube down Mr. Floyd’s throat after they arrived on scene, he said, but the nearest hospital was a five-minute drive away.

Mr. Nelson also noted that even doctors sometimes have trouble understanding that a patient who can talk is having trouble breathing. Mr. Floyd told police officers that he could not breathe, and in response, one officer told him that it takes oxygen to talk, implying that he must be able to breathe, something medical experts have said is false or misleading.

Dr. Bill Smock, the surgeon for the Louisville Metropolitan Police Department, also testified on Thursday, saying he saw no evidence of an overdose. “Mr. Floyd died from positional asphyxia, which is a fancy way of saying he died because he had no oxygen left in his body,” he said.

Mr. Floyd was alert and had a keen sense of space, which both indicate that he was not overdosing, Dr. Smock said. In addition, Mr. Floyd was begging for air — Dr. Smock called it “air hunger” — and said a person overdosing on fentanyl would typically have the opposite response, more like someone who falls asleep or slips into a coma.

Asked whether Mr. Floyd was suffering from a fentanyl overdose, Dr. Smock said, “That is not a fentanyl overdose. That is somebody begging to breathe.”

A forensic toxicologist, Daniel Isenschmid, who works at N.M.S. Labs in Pennsylvania, said that the drug profile found in Mr. Floyd’s system appeared to be more consistent with patients who were still alive, rather than those found in autopsies.