A retired Maryland medical examiner on Wednesday, April 14, lent support to the defense team theory that health conditions and drug ingestion were factors in George Floyd's death.

Dr. David Fowler also suggested that carbon monoxide could also have been a factor. He was the sole witness to testify Wednesday in the trial of Derek Chauvin, the former Minneapolis Police officer charged with murder and manslaughter in Floyd's May 25, 2020, death.

According to Fowler, Floyd's heart gave out while he was being restrained by Chauvin and other former Minneapolis police officers that night in May. More specifically, he said Floyd died of "sudden cardiac arrhythmia or cardiac arrhythmia due to his atherosclerotic and hypertensive heart disease."

Throughout the trial, defense attorney Eric Nelson has sought to elevate the role of drug use and heart health in Floyd's death above that of Chauvin's actions.

A long-time member and eventual chief of the Maryland medical examiner's office, Fowler retired in 2019 and works now as a consultant. He told the jury Wednesday he reviewed materials related to Floyd's death with a panel of forensic experts of which he is a member.

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As an expert witness in Chauvin's trial, Fowler has again become involved with a high-profile court case centered on the police killing of a Black man.

The Baltimore Sun reports that Fowler found Freddie Gray's 2015 death in city police custody to be a homicide. In a separate case, Fowler cleared police of responsibility for the 2018 death of teenager Anton Black, a case that bears a striking similarity to that of Floyd's.

Black's family alleges in a lawsuit against Fowler that he participated in a cover-up of the 18-year-old's death.

According to Fowler, Floyd did not die of asphyxia, or oxygen deprivation, as other medical experts who appeared in the trial have said. Fowler testified that Floyd had atherosclerosis, a disease typified by narrow arteries that Fowler said can cause the heart to stop suddenly.

Fowler also said that he considers Floyd's manner of death to be "undetermined." Medical examiners generally label manners of death as natural, accidental, suicidal, homicidal or undetermined.

That's a slight break with another witness's testimony. Hennepin County Medical Examiner Dr. Andrew Baker, who performed Floyd's autopsy, ruled his death a homicide. Baker did list the methamphetamine and fentanyl found in Floyd's system as "significant factors" in his death, and last week said Floyd's heart condition and subdual by law enforcement officers were "just more than (he) could take."

RELATED: Medical examiner testifies drugs, heart conditions were contributing causes in George Floyd's death

Fowler on Wednesday raised a new possibility: That carbon monoxide exposure could also have contributed to Floyd's death due to his being laid prone on the ground near the exhaust pipe of a running squad car the night he died.

That, in combination with Floyd's heart conditions — including high blood pressure and drug use makes it "very difficult to say which of those is the most accurate," Fowler said.

Under cross-examination by prosecutor Jerry Blackwell, however, Fowler agreed that Baker did not observe signs of carbon monoxide poisoning in Floyd's body. Floyd did not exhibit symptoms of a fentanyl overdose the night he died either, Fowler confirmed to Blackwell, nor did he have high levels of meth in his system.

In response to Fowler's earlier confirmation to Nelson that Floyd's autopsy found no signs of neck or back bruising, Blackwell cited medical literature stating that asphyxia can occur without bruising.

Fowler stood by his opinion that Chauvin did not occlude Floyd's airway by kneeling on the back of his neck.

"Would you agree that pressure on the soft side of the neck also narrows the side of the upper airway, the hypopharynx?" Blackwell asked.

"I have not seen any literature that indicates that that happens," Fowler replied.

But the doctor did agree that pressure to the chest can inhibit one's ability to draw in air, and that Floyd was "sandwiched" to the ground when city police officers were on top of him the night he died. Fowler additionally told Blackwell that there is generally time between the onset of sudden heart arrhythmia and death in which medical attention can be life-saving.

Should Floyd have received such care, Blackwell asked. Fowler answered in the affirmative.

Prosecutors have called into question whether Chauvin erred in not attending to Floyd's flagging health during their interaction in south Minneapolis last year. Barry Brodd, a former Bay Area police officer and use-of-force expert, testified this week that Chauvin had reason to keep Floyd in a prone position due to the "space limitations" posed by the squad car near which Floyd was restrained, and the crowd of bystanders observing the arrest.

RELATED: As defense presents case, use-of-force expert calls Chauvin's actions against Floyd 'justifiable'

Other developments

Earlier Wednesday, Judge Peter Cahill denied Nelson's motion to acquit Chauvin. It isn't uncommon for acquittal motions to be made after prosecutors finish presenting their case, which they did this week.

Jurors also heard briefly from Morries Hall, one of the two people Floyd was with at the time of his arrest. Cahill quashed a subpoena for Hall's testimony after his attorney successfully argued it could open him up to criminal charges. Hall appeared in-person at the Hennepin County Courthouse. He last appeared in court remotely from jail, where he was being held on unrelated charges.

Court is scheduled to resume 9:15 a.m. Thursday, April 15. Jurors could begin to deliberate on Chauvin's case as soon as Monday, April 19, Cahill has said.

RELATED: Floyd friend seeks to avoid testifying