The former police officer filmed kneeling on the neck of George Floyd has refused to testify at his murder trial.

This morning Derek Chauvin waived his right to testify to the jury about his part in the deadly arrest last May.

"I will invoke my Fifth Amendment privilege today," Chauvin said after briefly removing his mask, referring to the constitutional right against self-incrimination.

The remarks were his most extensive since his trial began with jury selection on March 8, and came as the most high-profile police misconduct case in decades nears its end.

The defence told Hennepin County District Judge Peter Cahill it would call no more witnesses after two days of testimony and would rest its case, which has focused on raising doubts about the cause of Floyd's death.

George Floyd died after a police officer knelt on his neck
George Floyd died after a police officer knelt on his neck

It is rare for defendants to take the stand in a criminal case because they face intense cross-examination by prosecutors and risk undermining their case and credibility.

Chauvin, who is white, was seen in bystander video kneeling on the neck of Floyd, a 46-year-old Black man in handcuffs, for more than nine minutes.

Floyd had been accused of using a counterfeit $20 bill to buy cigarettes.

The footage of his death sparked global protests against the disproportionate use of force by police against black people.

Chauvin's lawyers called an expert witness to tell the jury that Chauvin's use of force was appropriate.

A sketch of Chauvin made during the trial
A sketch of Chauvin made during the trial

In doing so he contradicted the Minneapolis police chief, who testified that it far exceeded an appropriate response.

They also called a forensic pathologist, former Maryland chief medical examiner Dr. David Fowler, who said Floyd really died of heart disease.

He also claimed that the exhaust fumes of the nearby police car may have also poisoned him.

Dr. Martin Tobin, a pulmonologist who testified as an expert witness for prosecutors, will return to the stand on Thursday in an effort to undermine Dr Fowler's testimony about carbon monoxide poisoning.

Defence lawyers for Chauvin are due to make their closing arguments on Monday
Defence lawyers for Chauvin are due to make their closing arguments on Monday

Prosecutors also said they had been contacted by Dr. Andrew Baker, the Hennepin County chief medical examiner who performed the autopsy on Floyd, to disclose previously unpublished test results that showed normal carbon monoxide levels in Floyd's blood.

The judge said prosecutors had been notified by the defence earlier this year that Chauvin would advance a theory of carbon monoxide poisoning.

Consequently he denied the request to admit the new evidence, saying it was too last-minute in a way that was prejudicial to Chauvin.

Cahill warned prosecutors that if Tobin even mentioned the existence of the results, he would declare a mistrial.

Tobin was questioned by prosecutors for only a few minutes, telling jurors that previously shared data showed that the level of carbon monoxide was "within the normal range.

Prosecutors from the Minnesota attorney general's office said they would call at least one rebuttal witness, and Cahill has previously advised jurors he expects both sides to present their closing arguments on Monday.

Jurors will then begin deliberating one of the most closely watched police misconduct cases ever seen in the United States.