George Floyd died of a sudden heart rhythm problem due to his heart disease while being restrained by police, a retired forensic doctor has testified for the defence at former officer Derek Chauvin's murder trial.
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That testimony contradicts several experts who say Floyd succumbed to a lack of oxygen.
Dr David Fowler on Wednesday said the fentanyl and methamphetamine in Floyd's system, and possible carbon monoxide poisoning from auto exhaust, were contributing factors.
He said Floyd also had high blood pressure and narrowing of the arteries.
"All of those combined to cause Mr Floyd's death," the former chief medical examiner for the state of Maryland said on the second day of the defence case.
He also testified that he would classify the manner of death "undetermined" rather than homicide as the county's chief medical examiner ruled.
Fowler said the death had too many conflicting factors, some of which could be ruled homicide and some that could be considered accidental.
Chauvin's lawyer Eric Nelson is trying to prove that the former Minneapolis police officer did what he was trained to do and that Floyd died because of his illegal drug use and underlying health problems.
Prosecutors say Floyd died because Chauvin's knee was pressed against Floyd's neck or neck area for more than nine minutes as the 46-year-old black man lay pinned to the pavement on his stomach last May, his hands cuffed behind his back.
Fowler listed a multitude of factors: Floyd's narrowed arteries, his enlarged heart, his use of methamphetamine and fentanyl, the stress of his restraint, his high blood pressure, the carbon monoxide, and a tumour or growth in his lower abdomen that can sometimes play a role in high blood pressure by releasing "fight-or-flight" hormones.
Fowler said all of those factors could have acted together to cause Floyd's heart to work harder and suddenly stop.
Previous witnesses have noted that a sudden heart rhythm problem does not necessarily produce visible signs on autopsy but can be inferred from circumstances such as a victim suddenly clutching one's chest and collapsing.
Nelson questioned Fowler extensively about carbon monoxide, which displaces oxygen in the bloodstream of people who breathe it in.
Fowler said it could have contributed to oxygen depletion in Floyd, noting that he was facing the tailpipe end of a vehicle. But there is no way to know for sure because, he acknowledged, Floyd's blood was never tested for carbon monoxide.
Several top Minneapolis police officials, including the police chief, have testified that Chauvin used excessive force and violated his training.
And a number of medical experts called by prosecutors have said Floyd died from a lack of oxygen because the way he was restrained restricted his breathing.
Fowler said the prone position alone does not affect a person's ability to breathe -- testimony that contradicts other witnesses who said the position Floyd was in, with his hands cuffed behind his back, was inherently dangerous.
He also testified that Chauvin's knee was not applied with enough pressure to cause any bruises or scrapes on Floyd's neck or back.
Chauvin, 45, is on trial on charges of murder and manslaughter in Floyd's death after his arrest on suspicion of passing a counterfeit $20 at a neighbourhood market.
The video of him as he gasped that he couldn't breathe touched off worldwide protests, violence and a furious examination of racism and policing in the US.
The defence hasn't said whether Chauvin will take the stand.
Australian Associated Press
