MINNEAPOLIS — A prominent forensic pathologist testified for Derek Chauvin’s defense Wednesday that George Floyd died of “sudden cardiac arrhythmia” because of existing heart disease and illicit drug use, contradicting prosecution experts who said Floyd succumbed to a lack of oxygen while pinned to the ground under the officer’s knee.

David Fowler, a former chief medical examiner for the state of Maryland, said he would not have categorized Floyd’s death a homicide, as an autopsy declared, saying there were too many conflicting factors to accurately determine the manner of death.

He also suggested Floyd’s exposure to exhaust from a nearby police squad car may have contributed to his death — though he later admitted during cross-examination from the prosecution that he wasn’t sure the vehicle was running.

Fowler cited a tumor in Floyd’s lower abdomen that he said could have added to Floyd’s existing high blood pressure and caused a “sudden surge” of adrenaline to his compromised heart.

“All of those combined to cause Mr. Floyd’s death,” testified Fowler, who now works as a private consultant and was a paid witness for the defense.

He cited the presence of fentanyl and methamphetamine in Floyd’s system — which he said could have been an “accidental” overdose — and his “significant natural” health issues, compared with being “restrained in a very stressful situation … [that] would be considered a homicide.”

“It’s very difficult to say which of those is the most accurate,” Fowler said. “So I would fall back to undetermined.”

But under intense cross-examination, Fowler conceded that Floyd, who he said had died “long, long before” an emergency room doctor pronounced him dead, could have been revived if Chauvin or other officers at the scene had given him “immediate medical attention.”

Asked whether he was critical of the decision by the officers to not perform lifesaving measures on Floyd, Fowler replied, “As a physician, I would agree.”

Prosecutor Jerry Blackwell questioned testimony by former Maryland chief medical examiner David Fowler during cross-examination on April 14. (The Washington Post)

Fowler’s testimony came as Chauvin’s defense tried for a second day to undermine two weeks of emotional testimony from prosecution witnesses who said Chauvin used excessive force when he knelt on Floyd’s neck and back for more than nine minutes while he was handcuffed, face down, on a Minneapolis street gasping for breath.

Defense attorney Eric Nelson has argued that Floyd died of a combination of drug intoxication and existing health problems, including heart disease and high blood pressure, not from the pressure of his client’s restraint. He has said Chauvin, a 19-year veteran of the department before he was fired in May, was following his training and department policy when he and other officers restrained Floyd — a claim that has been steadfastly denied by a litany of prosecution witnesses, including several of his former Minneapolis police colleagues.

But for a second day, it was unclear whether Chauvin’s witnesses were helping or hurting his defense, which could rest as soon as Thursday.

Fowler, who retired in 2019 after 17 years as Maryland’s chief medical examiner, faced withering cross-examination from prosecutor Jerry Blackwell, who pressed the pathologist on several of his findings, including his assertions that Chauvin’s knee was “nowhere near” Floyd’s airway and that Floyd’s speaking and moaning indicated the man’s airway was still open.

“You cannot make sound unless you are moving air,” Fowler testified.

Fowler said that Chauvin’s knee could not have caused positional asphyxia — as several prosecution experts have said — because there was no bruising or scrapes on Floyd’s neck or back. He did not address autopsy photos that showed deep abrasions on Floyd’s left front shoulder and hands — evidence prosecutors presented to the jury last week to show the force of Chauvin’s knee on Floyd’s body as he struggled for breath.

Citing his review of police body camera and other video of the scene, Fowler testified that he observed Chauvin to be using a “single knee technique” to restrain Floyd, positioning his knee mostly on the “bicep area or close to the left chest wall.”

He told the jury that even if Chauvin was using both of his knees to restrain Floyd, he believed the officer was applying only about 20 percent of his 140-pound body weight — “between 30 and 35 pounds” — to Floyd’s body.

But Fowler admitted under cross-examination that he did not take into account the gear Chauvin was wearing — including body armor and weapons — that prosecutors have said added 50 to 60 pounds to Chauvin’s total weight.

Martin Tobin, a Chicago-area pulmonologist who testified for the prosecution last week, told the jury that Chauvin appeared to be using most of his body weight to restrain Floyd and had placed about 92 pounds of weight on Floyd’s neck alone, narrowing his airway and causing “hypoxia,” or an oxygen deficiency that led to his death.

But Fowler, who said he had watched the testimony of Tobin and other prosecution experts as he prepared his own testimony, disputed those findings. He said he saw no evidence that Floyd was suffering from low oxygen in part because Floyd did not audibly acknowledge any vision problems, which he said was a common symptom of hypoxia.

“People describe little spots of light, a gray curtain coming down,” Fowler said. “[Floyd] complained of shortness of breath, but there was no indication that he made any statements that he was having difficulty in seeing things.” And Floyd’s shortness of breath, Fowler said, could have been caused by other factors.

Echoing another defense witness, use-of-force expert Barry Brodd, Fowler also cited studies claiming the prone position isn’t dangerous — studies he later conceded under cross-examination were conducted with young, healthy subjects and did not replicate the length or conditions under which Floyd was held.

During his nearly two hours of cross-examination, Blackwell repeatedly said he was not “trying to confuse the jury” — implying that was what Chauvin’s defense was attempting to do with Fowler’s testimony.

Blackwell took particular aim at Fowler’s claim that Floyd could have died of exposure to carbon monoxide, getting the former medical examiner to admit he wasn’t aware that the squad car was a hybrid vehicle or that it may not have been running. Fowler was the first expert to raise such a possibility.

“You haven’t seen any data or test results that showed Mr. Floyd had a single injury from carbon monoxide. Is that true?” Blackwell asked.

“That is correct,” Fowler said.

Fowler did not cite oxygen deprivation in his findings regarding Floyd’s cause of death, but under questioning from Blackwell, he conceded that low oxygen could have contributed to the fatal arrhythmia he said killed Floyd. Fowler agreed with Blackwell that it takes just four minutes for a lack of oxygen to “cause irreversible brain damage,” which in turn could stop the heart.

“And if a person dies as a result of low oxygen, that person is also going to die ultimately of a fatal arrhythmia, right?” Blackwell asked.

“Correct. Every one of us in this room will have a fatal arrhythmia at some point,” Fowler replied.

A year after stepping down as Maryland’s chief medical examiner, Fowler was sued, along with several other people and government entities in Maryland by the family of a young Black man who died during an encounter with police.

Anton Black, 19, died in 2018 after police officers responding to a call about a potential kidnapping in Greensboro, Md., wrestled him to the ground. Video footage captured the officers struggling with Black before pinning him to the ground.

Black’s family described the case as “chillingly similar” to Floyd’s in the federal lawsuit they filed in December. In the suit, they decried the medical examiner’s finding that Black’s manner of death was an accident.

Fowler and an assistant medical examiner signed the report, which noted that Black “suffered cardiac arrest while being restrained by law enforcement.” Their report also said “no evidence was found that restraint by law enforcement directly caused or significantly contributed to the decedent’s death.”

The Maryland Attorney General’s Office, which is listed as the attorney for Fowler and others from the medical examiner’s office named in the suit, filed a motion last week asking the court to dismiss the counts against them.

The case did not come up as Fowler took the stand in Minneapolis. Jurors seemed distracted and weary during his testimony, which took the entire day. Few took notes, and a juror fell asleep at one point.

Proceedings began Wednesday with Nelson moving for Chauvin’s acquittal, arguing that prosecutors had presented witnesses with conflicting testimony and had not proved their case — a typical move for the defense after the prosecution rests. Hennepin County District Judge Peter A. Cahill denied the motion.

Chauvin’s defense is expected to rest its case as soon as Thursday, far earlier than many had anticipated. Nelson has not said whether the former officer will take the stand.

Closing arguments in the case are expected Monday.

Berman reported from Washington.