Jerry Blackwell, a prosecutor with the Minnesota attorney general's office, told jurors that officers who wear the Minneapolis police badge pledge to never use "unnecessary force or violence."
"You will learn that on May 25, Mr. Derek Chauvin betrayed this badge when he used excessive and unreasonable force upon the body of George Floyd," Blackwell said.
He displayed a still image from a bystander's cellphone video of Chauvin, who is white, with his knee on the neck of Floyd, a 46-year-old Black man in handcuffs.
Prosecutors played the most widely seen bystander video to jurors on Monday.
Chauvin, dressed in a gray suit, a blue face mask and a blue shirt and tie, took pages of notes on a yellow legal pad as the dying moans of Floyd and the yelling of horrified onlookers filled the courtroom.
Chauvin, 45, has pleaded not guilty to second-degree murder, third-degree murder and second-degree manslaughter, with his lawyers arguing that he followed his training and that the main cause of Floyd's death, which the county examiner ruled a homicide, was a drug overdose.
He faces up to 40 years in prison if convicted on the most serious charge.
The Minneapolis Police Department fired Chauvin and the three other officers involved the day after the arrest. Floyd's death ignited a global protest movement over police brutality against Black people.