MINNEAPOLIS (AP) — The defense at the murder trial of former Officer Derek Chauvin in the death of George Floyd rested its case Thursday without putting Chauvin on the stand, presenting a total of two days of testimony to the prosecution’s two weeks.

Chauvin, his COVID-19 mask removed in a rare courtroom moment, informed the judge that he would not testify, saying he would invoke his Fifth Amendment right not to take the stand.

It would have been the first time Chauvin publicly told his side of the story.

“Is this your decision not to testify?” Judge Peter Cahill asked.

“It is, your honor,” Chauvin said.

Prosecution rebuttal testimony from an expert witness was expected to follow Thursday.

Closing arguments are set for Monday, after which the racially diverse jury will begin deliberating at the barbed-wire-ringed courthouse, with Minneapolis on edge against a repeat of the protests and violence that broke out last spring over Floyd’s death.

In a tense exchange before the jury was brought into the courtroom, the judge rejected prosecutors’ request to introduce new evidence that carbon monoxide levels in Floyd’s blood were within the normal range.

Prosecutor Jerry Blackwell said that after an expert defense witness had raised the issue Wednesday of possible carbon monoxide poisoning, prosecutors were informed that a test on Floyd’s blood gas had been done.

But the judge warned that if the prosecution’s expert witness “even hints that there are test results that the jury has not heard about, it’s going to be a mistrial, pure and simple. This late disclosure is not the way we should be operating here.”

The question of whether Chauvin would testify was the subject of weeks of speculation.

The risks were high: Testifying could have opened him up to devastating cross-examination, with prosecutors replaying the video of the arrest and forcing Chauvin to explain, one frame at a time, why he kept pressing down on Floyd.

But taking the stand could have also given the jury the opportunity to see or hear any remorse or sympathy he might feel. He would have been able to remove the mask he has had to wear at the defense table.

The only time Chauvin has been publicly heard defending himself was when the jury listened to body-camera footage from the scene last May. After an ambulance had taken Floyd away, Chauvin told a bystander: “We gotta control this guy ’cause he’s a sizable guy … and it looks like he’s probably on something.”

The decision not to testify was announced a day after a forensic pathologist testifying for the defense said that Floyd died of a sudden heart rhythm disturbance as a result of his heart disease. That contradicted prosecution experts who said Floyd succumbed to a lack of oxygen from the way he was pinned down.

Dr. David Fowler, a former Maryland chief medical examiner who is now with a consulting firm, said Wednesday the fentanyl and methamphetamine in Floyd’s system, and possibly carbon monoxide poisoning from auto exhaust, were contributing factors in the 46-year-old Black man’s death last May.

“All of those combined to cause Mr. Floyd’s death,” he said.

Fowler also testified that he would classify the manner of death “undetermined,” rather than homicide, as the county’s chief medical examiner ruled. He said Floyd’s death had too many conflicting factors, some of which could be ruled homicide and some that could be considered accidental.

Chauvin attorney Eric Nelson is trying to prove that the 19-year Minneapolis police veteran 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 the white officer’s knee was pressed against Floyd’s neck or neck area for 9 1/2 minutes as he lay on the pavement on his stomach, his hands cuffed behind him and his face jammed against the ground.

Fowler listed a multitude of factors or potential ones: Floyd’s narrowed arteries, his enlarged heart, his high blood pressure, his drug use, the stress of his restraint, the vehicle exhaust, and a tumor 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, suffer an arrhythmia, or abnormal rhythm, and suddenly stop.

Prosecutor Jerry Blackwell launched an aggressive cross-examination, attacking Fowler’s findings down the line. He got Fowler to acknowledge that even someone who dies from being deprived of oxygen ultimately dies of an arrhythmia.

A number of medical experts called by prosecutors have said Floyd died from a lack of oxygen because his breathing was constricted by the way he was held down. A cardiology expert rejected the notion that Floyd died of heart problems, saying all indications were that he had “an exceptionally strong heart.”

But Fowler said that Chauvin’s knee on Floyd was “nowhere close to his airway” and that Floyd’s speaking and groaning showed that his airway was still open. 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 charged with murder and manslaughter in Floyd’s death after his arrest on suspicion of passing a counterfeit $20 at a neighborhood market. The video of Floyd gasping that he couldn’t breathe as bystanders yelled at Chauvin to get off him triggered worldwide protests, violence and a furious examination of racism and policing in the U.S.

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