Dr David Fowler blames George Floyd's death on a heart problem in the trial of former Minneapolis police Officer Derek Chauvin.
"I will invoke my Fifth Amendment privilege today", Chauvin said after briefly removing his mask, referring to the constitutional right against self-incrimination, in his most extensive remarks since his trial began with jury selection on March 8.
After the defense rests its case, Judge Peter Cahill will allow the prosecution to call a witness to rebut some of the testimony by defense expert witness, Dr. David Fowler.
The outcome of the high-profile trial is being closely watched after video of the arrest of Floyd captured by a bystander prompted widespread outrage, setting off protests over race and police brutality across the USA and around the world.
Law enforcement veterans inside and outside the Minneapolis department testified for the prosecution that Chauvin used excessive force and went against his training, while medical experts said Floyd died of asphyxia, or lack of oxygen, because his breathing was constricted by the way he was held down.
He said Floyd's heart disease included high blood pressure and narrowing of the arteries.
The only time Mr Chauvin has been heard defending himself was when the jury listened to body-camera footage from the scene.
The decision of whether Mr Chauvin should testify carried risks either way. He told reporters that they had not expected Mr Chauvin to testify, saying the prosecution "would have chopped him down second by second" on the time he knelt on Mr Floyd.
But testifying could have also given the jury the opportunity to look at his unmasked face and see or hear any remorse or sympathy he might feel.
"It is, your honour", Chauvin said.
Prosecutors also recalled Dr. Martin Tobin, a lung and critical care expert, to the stand to poke holes in a defense witness' theory that carbon monoxide poisoning from a police car's exhaust could have contributed to Floyd's death. Nelson said prosecutors have known for weeks that Fowler had meant to bring up potential complications concerning carbon monoxide and should have sought to include the tests, conducted during Floyd's autopsy, earlier. Jamie Yuccas is following the trial in Minneapolis.
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