MINNEAPOLIS (WCCO) — A defense expert testified Wednesday that George Floyd’s manner of death cannot be determined because he believes there are many conflicting, contributing factors.

Dr. David Fowler was on the stand all day.

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The forensic pathologist said the factors contributing to death included Floyd’s drug use and his underlying heart conditions.

Another contributing factor Fowler cited was one not mentioned in court before — carbon monoxide poisoning from the exhaust of the police squad car.

Fowler testified that Floyd had to have suffered from carbon monoxide poisoning because his head was so close to the squad’s exhaust.

“You are not suggesting to the jury that Mr. Floyd died of carbon monoxide poisoning?” defense attorney Eric Nelson asked.

“Not exclusively, no,” Fowler said.

“Was Mr. Floyd’s blood tested for carbon monoxide?” Nelson asked.

“I could not find a reference to it,” Fowler said.

In fact, Floyd was never tested for carbon monoxide, but Fowler said because of his heart conditions Floyd was vulnerable to even a small amount.

“He had significant narrowing of all of his coronary arteries,” he said.

Fowler also testified about Floyd possibly consuming drugs.

“Did you determine whether there was the possibility that controlled substances were ingested at the time of approach by officers Kueng and Lane?” Nelson asked.

“Yes,” Fowler said. “In the back corner of Mr. Floyd’s mouth you can see what appears to be a white object.”

But the prosecution introduced stills of Floyd in Cup Foods.

“Do you see a white substance in George Floyd’s mouth?” prosecutor Jerry Blackwell asked.

“I can,” Fowler said.

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“Doesn’t it look remarkably similar to the white substance you were talking about?” Blackwell said.

“Yes, it looks very similar,” Fowler said.

“You are not then either telling or suggesting to the jury that the white substance was a pill, are you?” Blackwell asked.

“I never said it was a pill. I very carefully said that I could see a white structure in his mouth,” Fowler said.

The cause of death testimony seemed to captivate jurors. A pool report note said eight jurors took notes as Fowler repeatedly dismissed the significance of Chauvin’s knee on Floyd’s neck.

“Did you observe Mr. Chauvin’s knee obstructing the carotid artery of Mr. Floyd?” Nelson asked.

“The knee did not obstruct either carotid artery,” Fowler said, “and even if it had obstructed one, the carotid artery on the other side plus the two vertebral arteries in the neck would have supplied the brain with enough blood for it to function.”

The prosecution also got Fowler to say Floyd deserved care.

“Do you feel that Mr. Floyd should have been given immediate emergency attention to reverse the cardiac arrest?” Blackwell asked.

“As a physician I would agree,” Fowler said.

But the defense pushed back, clearly hoping Fowler’s most important conclusion could lead at least one juror to find reasonable doubt.

“How would you classify the manner of death?” Nelson said.

“So this is one of the cases where you have so many conflicting different manners,” Fowler said. “I would fall back to undetermined in this particular case.”

The judge ruled that the prosecution could bring a rebuttal witness to Fowler’s testimony. That could happen Thursday.

Also happening Thursday: the defense is expected to rest its case.

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The judge said earlier this week he would wait for closing arguments until Monday.