Cause of death at issue in Chauvin trial as prosecution questions medical examiner's findings

Prosecutors trying the former Minneapolis police officer charged with murder in George Floyd's death appeared to distance themselves last week from the medical findings on his cause of death, issued by the only doctor who performed an autopsy.

Special Prosecutor Jerry Blackwell told jurors last Monday that while Hennepin County Chief Medical Examiner Dr. Andrew Baker ruled Floyd's cause of death cardiac arrest, prosecutors would prove he died of asphyxia, or, lack of oxygen, while Chauvin knelt on his neck for more than nine minutes.

"This was … not a fatal heart event," Blackwell said in his opening statement. "He died one breath at a time over an extended period of time."

Some veteran attorneys and legal scholars said the prosecution appeared to draw a line between themselves and the medical examiner. Others said perhaps they were "shoring up" Baker's work, which concluded that Floyd's death was a homicide.

In a PowerPoint presentation during his opening statement, Blackwell displayed the names of six outside medical experts hired to help their case, including a forensic pathologist — Baker's job — whom Blackwell spoke about at length while mentioning Baker as an aside.

"Usually you hear about alternative experts — outside experts — from the defense," said former Ramsey County attorney Susan Gaertner. "Typically expert pathologists are hired by the defense to dispute or undermine the medical examiner's report.

"What is unusual is that, to some extent, the battle of the experts is within the state's case instead of between the state and the defense."

Chauvin's attorney, Eric Nelson, seized on the issue. To raise reasonable doubt, he told jurors in his opening statement, "The state was not satisfied with Dr. Baker's work so they have contracted with numerous physicians to contradict Dr. Baker's findings, and this will ultimately be another significant battle in this trial: What was Mr. Floyd's actual cause of death?"

He noted that Baker was the only person to perform an autopsy on Floyd.

"Dr. Baker found none of what are referred to as the telltale signs of asphyxiation," said Nelson. "There was no evidence that Mr. Floyd's airflow was restricted and he did not determine [it] to be a positional or mechanical asphyxia death."

Nelson argued that Floyd died of a cardiac arrest resulting from drug use and pre-existing health issues, including heart disease and high blood pressure.

Chauvin is on trial for second-degree murder, third-degree murder and second-degree manslaughter.

Bystander Darnella Frazier's graphic video showing Chauvin kneeling on Floyd last May 25 while he repeatedly said he couldn't breathe has been played in court several times, but a medical ruling on cause of death is still crucial to the case, some attorneys said.

Prosecutors have yet to call Baker or their medical experts to the witness stand. Blackwell told jurors they would hear from "a number of experts" and pathologist Dr. Lindsey Thomas.

"This is going to be the most fascinating part of the trial," said defense attorney Tom Heffelfinger, a former assistant Hennepin County attorney and U.S. attorney for the district of Minnesota. "Every one of those people they put on just creates a little more doubt. It makes it easier to argue about the cause of death, and you've got to have a cause of death."

Medical examiners in Minnesota work independently of law enforcement and prosecutors. They determine the cause and manner of death, but make no determination about legal culpability.

However, as the authority legally mandated to perform autopsies and issue reports about sudden, suspicious or unexpected deaths, their findings historically form the bedrock of criminal cases and are largely undisputed by prosecutors.

"It seemed to me that essentially the prosecution is going to take the position that Dr. Baker's autopsy report is incorrect or can be explained more clearly," said Mitchell Hamline School of Law emeritus professor Prof. Joe Daly. "It's extremely unusual … to cast doubt on your own medical examiner."

Baker's findings that Floyd's cause of death was "cardiopulmonary arrest complicating law enforcement subdual, restraint, and neck compression" sparked public outrage when they were released last June 1. Many, including attorneys for Floyd's family, believed Floyd died of asphyxiation and criticized Baker's ruling. An emergency fence and concrete barricades were erected around Baker's downtown Minneapolis office two days after he issued his results; they remain standing.

Baker listed hardening and thickening of the artery walls, heart disease and drug use as "other significant conditions." Fentanyl and methamphetamine were also found in Floyd's system.

Baker ruled the manner of death a homicide, a death that occurs at the hands of another person.

Baker reviewed his findings in a meeting last December with the Minnesota Attorney General's Office, which is prosecuting the case.

"It appeared to Dr. Baker that the pressure to the neck was coming from the back or posterior lateral portions of the back, and none of these strictures would impact breathing or cause loss of consciousness," said a document summarizing the meeting. " … Dr. Baker found it important that Floyd had narrowing of coronary arteries: 75-80% narrowed. This would put him at risk for a sudden cardiac arrest."

In the meeting Baker, reportedly cited a study that found that placing 200 pounds of weight or more on a healthy person did not have an "observable impact on breathing."

He reportedly referenced a recent study that said positional restraint did not lead to "ventilatory or cardiac failure."

"Dr. Baker offered that one possibility for the pathway of Floyd's death is that Floyd's heart was starting to fail because of the stress, drugs, enlarged heart, and [heart] disease," said a summary of the meeting. "He said that once the heart starts to fail … one of the symptoms is the perception that you cannot breathe."

Nelson told jurors they would hear about "several" interviews between Baker and investigators, "and some of this evidence is extremely important to the final determination of Mr. Floyd's cause of death."

Blackwell directed jurors to Frazier's video in building his case for cause of death.

"I would tell you that you can believe your own eyes that it's a homicide, it's murder," Blackwell said. "You can believe your own eyes."

Prosecutors don't have to prove that Chauvin's actions alone caused Floyd's death, according to Minnesota guidelines for jury instructions. According to the state and the defense's proposed jury instructions, "  'To cause' means to be a substantial causal factor in causing the death. … The fact that other causes contribute to the death does not relieve the defendant of criminal liability."

Being restrained and pressed upon while lying flat on your stomach can restrict the intake of oxygen and output of carbon dioxide, and reduce blood flow through the heart, leading to a fatal cardiac arrest, said cardiologist Dr. Alon Steinberg, chief of cardiology and medicine at Community Memorial Hospital, based in California.

Steinberg, who recently published a paper reviewing scientific literature on prone restraint, described Floyd's death as a "prone restraint cardiac arrest."

"When people are in prone restraint and they die, it's more accurate that it's a cardiopulmonary arrest as [Baker] says," said Steinberg. "It's not asphyxia."

Prone restraint prevents the rib cage and diaphragm from expanding, thereby reducing breathing ability and causing a dangerous build up of carbon dioxide in the body that is a "much bigger issue" than the lack of oxygen, he said. An accumulation of the waste gas causes metabolic acidosis, or, an overproduction of acid, he added.

Steinberg said Chauvin kneeling on Floyd's neck could have also reduced blood flow from the head into the heart, and former officer J. Alexander Kueng kneeling on Floyd's back could have reduced blood flow from the lower body into the heart.

Kueng and two other officers at the scene — Thomas Lane and Tou Thao — are each charged with aiding and abetting second-degree murder and manslaughter in the case and are scheduled to be tried Aug. 23. All four defendants, who were fired, are out on bond.

Asphyxiation is commonly used to describe such deaths, Steinberg said, adding that they often don't leave behind evidence of physical damage in the heart or in the body's tissues.

"It [is] more complex than [asphyxiation], and death is due to multiple factors including acidosis, decreased cardiac output and decrease in ventilation," he said.

Blackwell told jurors Thomas will testify about the "limitations of pathology" and address how, in over half of deaths from a lack of oxygen, no evidence is left behind in the body's tissues.

It could pose a risk to the prosecution's case to distance themselves from the in-house medical expert, said defense attorney Mike Padden.

"It absolutely can be a problem because he's the doctor who did the autopsy," Padden said. "They're making a strategy decision that they're moving completely away from him."

An abundance of complex medical testimony could also overwhelm jurors. The defense has 15 medical experts listed as potential witnesses; it's unknown how many will be called to testify.

"I think there's going to be far too much reliance … put on the medical testimony," said defense attorney A.L. Brown. "Jurors try very hard to understand things, and they're put in an impossible position to try to understand very complicated things."

Staff writer Libor Jany contributed to this report.

Chao Xiong • 612-270-4708