A Minneapolis homicide investigator who went to the crime scene after George Floyd's deadly arrest at a city intersection testified against his former colleague Derek Chauvin, who kept his knee on Floyd's neck for nine minutes.
Mr Chauvin was fired by the city's police department the day after he was captured on video on top of a dying Mr Floyd in a scene that sparked protests against police brutality around the world.
"Once a person is cuffed, the threat level goes down all the way," Lieutenant Richard Zimmerman told the jury after prosecutors called him to testify.
"They're cuffed. How can they really hurt you, you know? If your knee is on a person's neck, that can kill them," he said.
Mr Chauvin (45) has pleaded not guilty to murder and manslaughter charges.
According to testimony heard on the fifth day of the trial, Lieut Zimmerman, who joined the Minneapolis Police Department in 1985 and is now its most senior officer, was at home on May 25th, 2020, when he was called to the intersection outside Cup Foods, where Mr Floyd was suspected of passing a fake $20 earlier in the evening.
He arrived just before 10 pm, about half an hour after Mr Floyd had been declared dead at a downtown hospital, and said he helped ensure that evidence was properly secured and any witnesses were found.
Lieut Zimmerman said officers were responsible for the care of anyone they arrested.
"His safety is your responsibility, his wellbeing is your responsibility," he told the jury.
He described how officers are trained only to respond to any threat with a proportionate amount of force, and warned of the dangers of leaving a person in a prone position.
"If your knee is on a person's neck, that can kill them," he said.
