One of three ex-Minneapolis policemen present at the death of George Floyd will testify in his own defence in a federal civil case against him and his colleagues.
The charge that Thomas Lane deprived Mr Floyd of his civil rights is “a perversion of justice”, his lawyer said.
Mr Lane, 38, and ex-officers J Alexander Kueng and Tou Thao are also facing state criminal charges.
The federal trial opened on Monday.
In her opening argument, Samantha Trepel, the government prosecutor, said that the three men should be held accountable for failing to act as Mr Floyd had his neck pinned to the ground by senior officer Derek Chauvin.
“These three CPR-trained defendants stood or knelt next to Officer Chauvin as he slowly killed George Floyd right in front of them,” she said.
The government is seeking to prove that the ex-officers showed “deliberate indifference to [Mr Floyd’s] serious medical needs” during the attempted arrest, thus depriving him of his right against illegal search and seizure under the Fourth Amendment of the US Constitution.
But Eric Gray, Mr Lane’s lawyer, described him on Monday as a “gentle giant” who “did everything possible to help George Floyd”.
It is rare for US police officers to be charged under civil rights statutes, and the trial could ultimately expand how officers are held liable for excessive use of force.
Twelve jurors and six alternates were selected for the trial last week.
Video evidence shows that, as Chauvin pressed his knee into Mr Floyd’s neck, Mr Lane restrained his legs, Mr Kueng, 27, held his torso, and Mr Thao, 35, warned bystanders to keep away from them.
Mr Lane and Mr Kueng’s defence teams are expected to argue that fault lies with Chauvin, the senior officer. Their lawyers have pointed out that the two men were rookies in their first week on the job, with Chauvin as their training officer.
A criminal complaint against Mr Lane mentions he twice asked Chauvin whether they should turn Mr Floyd over into a side recovery position and was rebuffed both times.
The trial is expected to last about four weeks.
Legal experts say prosecutors could also ask Chauvin to take the stand against his colleagues.
Convicted of murder and manslaughter last June, Chauvin is serving 22 1/2 years in state prison.
He is also awaiting federal sentencing for his own civil rights charges, after accepting a plea deal in December in order to avert a second trial.
Lawyers for the Floyd family said the trial would be “another painful experience” but “another milestone in the long, slow journey to justice for George Floyd and his family”.
Mr Floyd’s murder led to racial justice protests worldwide in 2020.