MINNEAPOLIS – A veteran medical examiner testified Friday in Derek Chauvin's murder trial that George Floyd died from a lack of oxygen from being restrained by Minneapolis police officers.
"In this case I believe the primary mechanism of death is asphyxia, or low oxygen," said Dr. Lindsey Thomas, a medical examiner of 37 years who retired from the Hennepin County Medical Examiner's office in 2017 and still works as a forensic pathologist in Reno and Salt Lake City.
Thomas explained that although Floyd's heart stopped, he didn't die from a heart attack. She said that the sheer volume of videos of Floyd's death was "absolutely unique" in that she'd never had a case so thoroughly documented, and it helped her arrive to her determination of how Floyd died.
"The activities of the law enforcement officers resulted in Mr. Floyd's death and specifically those activities were the subdual restraint and the neck compression," she said.
"What I observed from all of these videos is this was not a sudden death," Dr. Lindsey Thomas testified. "It's not like snow shoveling when someone clutches their chest and falls over. There was nothing sudden about his death."
She later said with certainty, "There's no evidence to suggest he would have died that night expect for the interactions with law enforcement."
Thomas's declaration runs counter to the assessment of Baker, who according to court documents, said in a meeting with the FBI that he could not say whether Floyd would have lived "but for" the officers' use of force.
"Baker did not believe that the prone position was any more dangerous than other positions based on an article or journal he had read," said a summary of the meeting.
Thomas was the first witness on the same day the jury was expected to hear testimony from Hennepin County Medical Examiner Dr. Andrew Baker, who performed an autopsy on Floyd after he died under the knee of the since-fired Minneapolis police officer on May 25, ruled the cause of death as "cardiopulmonary arrest complicating law enforcement subdual, restraint, and neck compression." Thomas, who helped train Baker when he was a resident in the office, said she agreed with Baker's determination on the cause of death.
He also listed hardening and thickening of the artery walls, heart disease and illicit drug use as "other significant conditions." Fentanyl and methamphetamine were also found in Floyd's system, Baker's autopsy results noted.
Thomas also joined other expert witnesses before her saying illicit drug use did not kill Floyd.
Prosecutor Jerry Blackwell spent a fair amount of time having Thomas explaining some of the limitations of an autopsy and what advantages she had in her research of Floyd's death.
She zeroed in on why Floyd's health challenges and drug use were included by Baker and explained that such information is valuable for a "public health purpose" and not considered a direct cause of death.
"In any given case, we aren't just thinking of this particular person," Thomas said. "[Autopsy results] list disease processes or drugs that are present at the time of death, but we don't believe they directly contributed to the cause of death."
She also downplayed the autopsy failing to mention lack of oxygen, or asphyxia, despite she and others who have testified to this being the direct cause of death.
"I tend not to use it," she said, while also pointing out that there is no test during an autopsy to detect this cause. As an example, Thomas said, "I wouldn't say asphyxia during hanging. I would just say hanging."
She revisited ground covered by previous medical expert witnesses concerning injuries on Floyd's body that revealed his struggle to reposition himself to allow him to better breathe: scapes on his knuckles, face and shoulders, for example.
The judge then had photos of the injuries distributed to the jurors, and Thomas explained what they depicted and why including that the images "are consistent that he is pushing himself so he can get in a position to breathe."
Thomas testified that she wasn't being paid to serve as an expert. "You reached out to me and 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 explain what I think happened," she said.
Baker's expected testimony Friday could pose challenges for both the state and defense if it echoes the information exchanged in at least a half-dozen meetings he had with prosecutors leading up to the trial.
Documents obtained by the Star Tribune show Baker expressed skepticism that placing Floyd face down on the street with three officers on top of him would be "any more dangerous than other positions." He also revealed that he did not review videos from the scene, according to the documents.
On that point, Thomas testified that the bodily stress of being restrained in a prone position must be taken into account and has been absent in controlled research in this area.
"Mr. Floyd was already in a position where he was experiencing breathing and getting enough oxygen in this body," she said. "On top of that, now there's the physiological stress that's putting increased demand on his heart, lungs and muscles. ... He's using his strength to get himself into a position where he can breathe."
Add in the release of adrenaline, rapid breathing and other bodily reactions, she said, "it's kind of a double whammy to his heart, lungs, his muscles and his whole system."
In cross examination by defense attorney Eric Nelson, Thomas acknowledged that Floyd had a slightly enlarged heart that would require more blood and that he had significantly narrowed arteries.
With those factors, along with the stress Floyd endured "the heart has to work very, very hard in this case, right?" Nelson asked.
"Let's take the police out of this," he continued. "Let's assume you found Mr. Floyd dead in his residence, no police involvement, no drugs, the only thing you found were these facts about his heart. What would you conclude is the cause of death?" Nelson asked.
"In those very narrow circumstances I would probably conclude that the cause of death was his heart disease," Thomas said.
Before testimony resumed Friday, District Judge Peter Cahill said he has one issue to deal with and then summoned in a juror. Cahill then took the proceedings off the livestream but allowed two news reporters to remain and document.
Cause of death has provided a sharp divide between the state and the defense. Defense attorney Nelson has argued that Floyd died of a cardiac arrest, illicit drug use and various chronic health problems.
Chauvin for the first time had a spectator in the courtroom, an unidentified woman who sat in the family representative seat.
A prosecution witness called Thursday concluded that Floyd died from a lack of oxygen while being held stomach-down and handcuffed on the pavement for more than 9 minutes.
Dr. Martin Tobin, a leading lung expert who has written textbooks and specialized in respiratory and critical care medicine for decades, said the oxygen that Floyd begged for minute after minute "caused damage to his brain that we see, and it also caused a [pulseless electrical activity] arrhythmia that caused his heart to stop."
Chauvin is on trial for second-degree murder, third-degree murder and manslaughter. The three other fired officers — J. Alexander Kueng, Thomas Lane and Tou Thao — are scheduled for trial in August on charges of aiding and abetting him. Thao held off the bystanders while the others restrained Floyd.
Tobin said his extensive review of the viral bystander video, footage from officers' body-worn cameras and on-the-street surveillance and investigative evidence led him to this conclusion:
Chauvin kept his knee on Floyd's neck for three minutes and 27 seconds after Floyd took his final breath.
In his cross-examinations, Nelson worked to show that Floyd could have died from a heart attack or overdose caused by drugs and underlying health problems, including arterial blockages. When prosecutor Jerry Blackwell asked Tobin whether Floyd's pre-existing health conditions had anything to do with his death, the doctor replied, "none whatsoever."
As the slowed-down bystander video was shown of Floyd's face, Tobin described the death: "You can see slight flickering and then it disappears, so one second he's alive and one second he's no longer. That's the moment the life goes out of his body."
A follow-up witness supported much of what Tobin said. Dr. Bill Smock, the police surgeon of the Louisville Police Department, also concluded that Floyd died from a lack of oxygen and not a fentanyl overdose. Smock said people who overdose on fentanyl become sleepy, snore, have constricted pupils and their breathing rate falls. With Floyd, Smock said, "that is not a fentanyl overdose. That is someone begging to breathe."
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(Star Tribune staff writers Rochelle Olson, Libor Jany and Chao Xiong contributed to this report.)
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