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Getting to the truth about George Floyd’s cause of death

In the Derek Chauvin murder trial, experts’ demeanor is as important as their testimony

The moment of truth has arrived in the Derek Chauvin murder trial: testimony about what caused the death of George Floyd. But like several other aspects of the case, truth can be distorted by the nature of our criminal justice system.

The fatal factor seems excruciatingly obvious to many who watched the video of Floyd dying with the Minneapolis policeman’s knee on his neck. Floyd begged Chauvin for mercy, said he was about to die, told his family goodbye, then went limp. But the workings of the human body are complex and subject to interpretation, and Chauvin is facing a 40-year prison sentence. Chauvin’s lawyer, Eric Nelson, says that Floyd died from a combination of drugs in his system and health problems.

Prosecutors have presented expert witnesses who testified that the main cause of Floyd’s death in May was a lack of oxygen. Chauvin’s experts are expected to say the opposite later in the trial. The outcome of this battle of the experts, like several other aspects of this case, strays from our idealized version of justice being determined strictly by the “facts.”

Instead, convincing the jury that Chauvin killed Floyd hinges on how well the information is presented. How likable are the doctors and toxicologists who take the stand? How clearly do they explain difficult medical subjects? How do they respond to Nelson’s attempts to undermine their conclusions? The jurors’ answers to these questions likely will play a major role in whether the white ex-cop goes to prison for killing this Black man.

Defense attorney Eric Nelson (left) and the defendant, former Minneapolis police officer Derek Chauvin (right), listen as Hennepin County Judge Peter A. Cahill presides on April 8 in Minneapolis.

Court TV via AP, Pool

“The jury tends to believe the expert who can better communicate [rather] than the one with the better opinion,” said Temple University law and business professor Samuel Hodge Jr., who published a law review paper on the Floyd autopsy and whose books include Anatomy for Litigators. Hodge’s paper on Floyd describes how medical experts can legitimately reach different conclusions from the same set of evidence.

There also are ways to work the system. “The independent expert witness, in all candor – there are hired guns,” Hodge said. “I was a civil litigator for 40 years, and I knew the plaintiff’s counsel was going to send the client to a doctor who was going to say what they wanted him to say. Likewise, I’m going to send somebody to a person who has a defense side to them.

“That’s the game. That’s how it works. That’s why expert testimony is just a piece of the evidence that a jury can accept or not accept.”

Two autopsies were performed on Floyd’s body. The county medical examiner ruled his death a homicide, citing “cardiopulmonary arrest complicating law enforcement subdual, restraint and neck compression,” plus the presence of fentanyl and methamphetamine in Floyd’s system, underlying heart disease and a positive COVID-19 test result. Pathologists hired by Floyd’s family reported that he died of asphyxiation.

On Thursday, the prosecution began presenting their series of doctors. The first, Martin Tobin, is a lauded Chicago pulmonologist who has studied breathing for 46 years. His gray hair, kindly manner and Irish accent seemed endearing, while his confident answers sounded decisive. Having been paid to testify in many trials – although this was his first criminal case, and he did not accept any payment for his work – Tobin knew how to disagree with Nelson’s cross-examination without appearing argumentative or petty. Trial observers raved about Tobin’s command of the courtroom, including when he instructed jurors to feel their own throats. Nelson objected, and the judge told jurors any self-examination was optional.

Tobin stated the cause of death without equivocation: “George Floyd died from a low level of oxygen. This caused damage to his brain that we see, and it also caused … arrhythmia that caused his heart to stop.

“You’re seeing here fatal injury to the brain from a lack of oxygen,” Tobin said.  

Another prosecution witness, forensic toxicologist David Isenschmid, testified that the percentage of metabolized fentanyl in Floyd’s blood shows he did not die of an overdose. He said intoxicated drivers have been pulled over and found to have higher levels of fentanyl in their blood than Floyd. Bill Smock, a police surgeon and emergency medicine professor in the Louisville Police Metro Department, was paid $300 per hour by the prosecution for his review of the case and testimony. He detailed several reasons Floyd did not die of a fentanyl overdose or “excited delirium,” another theory put forth by Chauvin’s team.

On Friday, after testimony from another forensic pathologist, Lindsey Thomas, the medical examiner who performed the autopsy finally took the stand and offered a different description of what killed Floyd.

Andrew Baker said he did not watch the video before the autopsy to avoid bias. He testified that Floyd died from a combination of the stress of being subdued by police, drugs, and his health problems. Previous witnesses had testified that drugs and health problems played no role. Baker said “those are not direct causes. Those are contributing causes.”

Baker described Floyd as having severe heart disease, and said that as the encounter with Chauvin sent stress hormones and adrenaline coursing through Floyd’s body, “the law enforcement subdual restraint and the neck compression was just more than Mr. Floyd could take by virtue of those heart conditions.”

“It was the stress of that interaction that tipped him over the edge, given his underlying heart disease and his toxicological status,” Nelson said.

Later in the trial, the defense will present its own experts. For now, Nelson used his cross-examinations to bring up Floyd’s drug use and health problems – cardiovascular disease, a severely blocked artery, high blood pressure – trying to provide jurors with a reasonable doubt that Chauvin choked the life out of Floyd. Over and over, he made statements disguised as questions to which the only possible answer was “yes”: There is no reasonable use for methamphetamines bought off the street? There was no bruising found on Floyd’s neck? You did not weigh Mr. Chauvin on the day of this incident, so you don’t know exactly how much force he exerted on Mr. Floyd?

It’s hard to tell how the jurors felt about all this. They are not being shown on the Court TV livestream, but pool reporters in the courtroom described them taking plentiful notes and paying close attention to the charts and illustrations. One of the jurors is a nurse, who was described as “riveted” by Tobin’s testimony.

The Irish doctor was a star witness, with his askew tie and crooked glasses belying the precision of his testimony. He cited percentages, weights and ratios from memory. Asked by Nelson why there were no bruises on Floyd’s neck, he responded: “When I go to church, I sit on a hard bench. I don’t get bruising on my bottom.” He even narrated a segment of the infamous video by identifying the exact moment of Floyd’s death, when his eyes flickered: “One second he’s alive and one second he’s no longer. That’s the moment the life goes out of his body.”

After that moment, Tobin testified, Chauvin’s knee remained on Floyd’s neck for another 3 minutes and 27 seconds.

Jesse Washington is a journalist and documentary filmmaker. He still gets buckets.