The Minneapolis police chief has testified that now-fired officer Derek Chauvin violated departmental policy in pinning his knee on George Floyd's neck and keeping him down after Floyd had stopped resisting and was in distress.
Continuing to kneel on Floyd's neck once he was handcuffed behind his back and lying on his stomach was "in no way, shape or form" part of department policy or training, "and it is certainly not part of our ethics or our values," Police Chief Medaria Arradondo said on Monday, day six of Chauvin's murder trial.
Arradondo, the city's first black chief, fired Chauvin and three other officers the day after Floyd's death last May and in June called it "murder".
While police have long been accused of closing ranks to protect fellow members of the force who have been accused of wrongdoing, some of the most experienced members of the Minneapolis department have taken the stand to openly condemn Chauvin's treatment of Floyd.
As jurors watched in rapt attention and scribbled notes, Arradondo testified not only that Chauvin, a 19-year veteran of the force, should have let Floyd up sooner but that the pressure on Floyd's neck did not appear to be light to moderate, as called for under the department's neck-restraint policy; that Chauvin failed in his duty to render first aid before the ambulance arrived; and that he violated policy requiring officers to de-escalate tense situations if they can to avoid or minimise the use of force.
"That action is not de-escalation," the police chief said.
"And when we talk about the framework of our sanctity of life and when we talk about our principles and the values that we have, that action goes contrary to what we are talking about."
On cross-examination, Chauvin lawyer Eric Nelson asked Arradondo the last time he actually arrested a suspect.
"It's been many years," the chief acknowledged.
Arradondo's testimony came after the emergency room doctor who pronounced Floyd dead testified that he theorised at the time that Floyd's heart most likely stopped because of a lack of oxygen.
Bradford Langenfeld, who was a senior resident on duty that night at Hennepin County Medical Center and tried to resuscitate Floyd, took the stand as prosecutors sought to establish that it was Chauvin's knee on the black man's neck that killed him.
Langenfeld said Floyd's heart had stopped by the time he arrived at the hospital.
The doctor said that he was not told of any efforts at the scene by bystanders or police to resuscitate Floyd but that paramedics told him they had tried for about 30 minutes.
Under questioning by prosecutor Jerry Blackwell, Langenfeld said that based on the information he had, it was "more likely than the other possibilities" that Floyd's cardiac arrest - the stopping of his heart - was caused by asphyxia, or insufficient oxygen.
Chauvin, 45, is charged with murder and manslaughter in Floyd's death.
The white officer is accused of pressing his knee into the 46-year-old man's neck for nine minutes and 29 seconds, outside a corner market, where Floyd had been accused of trying to pass a counterfeit $US20 bank note for a pack of cigarettes.
The defence argues that Chauvin did what he was trained to do and that Floyd's use of illegal drugs and his underlying health conditions caused his death.
Nelson, Chauvin's laywer, asked Langenfeld whether some drugs can cause hypoxia, or insufficient oxygen.
The doctor acknowledged that fentanyl and methamphetamine, both of which were found in Floyd's body, can do so.