Updated April 12, 2021 at 1:35 PM ET
The trial of former Minneapolis police officer Derek Chauvin on murder charges is entering its third week of testimony. The prosecution is nearing the end of its case, and Chauvin's defense is expected to begin presenting its case this week.
Prosecutors have been focusing on medical experts as they try to prove that Chauvin's actions killed George Floyd. Chauvin held his knee on Floyd's neck for nine minutes and 29 seconds on Memorial Day last year.
Dr. Jonathan Rich, a cardiologist at Northwestern Memorial Hospital in Chicago, gave expert testimony on his analysis of how George Floyd died.
"Mr. George Floyd died from a cardiopulmonary arrest. It was caused by low oxygen levels. And those low oxygen levels were induced by the prone restraint and positional asphyxiation that he was subjected to," Rich said.
Rich said he came to his conclusions based on medical records, interviews, videos and the autopsy report.
He said he investigated two other possible causes: a primary heart event (that is, one not caused by something else) or a drug overdose. He concluded that neither was the cause of death in this case.
"After reviewing all the facts and evidence in the case, I can state with a high degree of medical certainty that George Floyd did not die from a primary cardiac event and he did not die from a drug overdose," Rich said.
The entire jury appeared to be taking notes furiously at this point, reporters in the courtroom said.
There was no evidence in the autopsy that Floyd died of a heart attack, Rich said, and he said he saw no evidence that the cause of death originated in Floyd's heart.
He said he found it notable but not unusual that Floyd had coronary artery disease. And, he said, "I see no evidence at all to suggest that a fentanyl overdose caused Mr. Floyd's death."
Rich named two reasons for this belief. Through chronic use, Floyd had apparently developed a high tolerance to opiates and could handle high amounts without being very affected, according to a report from one visit to the emergency room.
Possibly more important, Rich said, is that he saw no signs of opiate overdose in Floyd, such as lethargy, slurred speech, or difficulty to arouse. Instead, Floyd was alert, conversant and walking around before his death.
Rich said he believes that methamphetamine "played no substantive role" in Floyd's death. There was a relatively low level of methamphetamine in Floyd's system, he said, and he found it very unlikely that it would have triggered this major event in Floyd's system.
"I believe that Mr. George Floyd's death was absolutely preventable," Rich said.
At several junctures, there were opportunities to save Floyd's life, Rich said. The first was if officers had not put Floyd in the restraint position. And second, when Floyd said he was having difficulty breathing and there were signs he was worsening, Rich said, officers could have put him into a recovery position to aid his breathing.
Over the objections of the defense, prosecutor Jerry Blackwell asked: Would Mr. Floyd have lived if not for Chauvin's subdual and restraint of him for nine minutes and 29 seconds on the ground?
"Yes, I believe he would have lived," Rich said.
During cross-examination, Chauvin's attorney Eric Nelson asked a number of questions about how Floyd's narrowed arteries and drugs in his system might have played a role in his death.
Nelson also seemed to open up a potential line of argument as he asked Rich: Had Mr. Floyd simply gotten in the back of the squad car, would he have survived?
"Had he not been restrained in the way in which he was, I think he would have survived that day," Rich answered. "I think that he would have gone home or wherever he was going to go, had he not been subjected to the prone and positional restraint that he was."
"In other words, if he'd gotten in the squad car, he'd be alive," Nelson said.
"I think my answer remains the same. Anything other than that scenario he was subjected to. ... I have no reason to believe he would not have survived that day," Rich responded.
Last week, the Hennepin County medical examiner testified that he deemed Floyd's death to be a homicide. And Floyd had serious heart issues, Dr. Andrew Baker told the court.
"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," Baker told the jury.
Nelson asked questions about Floyd's health problems and the fentanyl and methamphetamine in his system at the time of his death. Baker stated that he thought those factors played a role in his death, but were not the direct cause.
NPR's Merrit Kennedy contributed to this report.
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