MINNEAPOLIS — The Minneapolis police chief testified Monday 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 Day 6 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 — the “blue wall of silence,” as it’s known — 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 minimize 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 attorney 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 theorized at the time that Floyd’s heart most likely stopped because of a lack of oxygen.

Dr. 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 it was Chauvin’s knee on Floyd’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 May 25. The white officer is accused of pressing his knee into the 46-year-old man’s neck for 9 minutes, 29 seconds, outside a corner market, where Floyd had been accused of trying to pass a counterfeit $20 bill for a pack of cigarettes.

The defense 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 attorney, sked 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.

The county medical examiner’s office ultimately classified Floyd’s death a homicide — that is, a death at the hands of someone else.

The full report said Floyd died of “cardiopulmonary arrest, complicating law enforcement subdual, restraint, and neck compression.” A summary report listed fentanyl intoxication and recent methamphetamine use under “other significant conditions” but not under “cause of death.”

Under cross-examination from Nelson, Langenfeld said Floyd’s carbon dioxide levels were more than twice as high as levels in a healthy person, and he agreed that that could be attributed to a respiratory problem. But on questioning from the prosecutor, the doctor said the high levels were also consistent with cardiac arrest.

Langenfeld said that “any amount of time” a patient spends in cardiac arrest without immediate CPR decreases the chance of a good outcome. He said there is an approximately 10% to 15% decrease in survival for every minute that CPR is not administered.

Prosecutor Steve Schleicher noted that while some people may become more dangerous under the influence of drugs or alcohol, some may actually be “more vulnerable.” Arradondo agreed and acknowledged that this must also be taken into consideration when officers decide to use force.

Before he was pinned to the ground, a handcuffed and frantic Floyd struggled with police who were trying to put him in a squad car, saying he was claustrophobic.

Arradondo said officers are trained in basic first aid, including chest compressions, and department policy requires them to request medical assistance and provide necessary aid as soon as possible before paramedics arrive.

Officers’ first aid training is “very vital because those seconds are vital,” Arradondo said, adding: “And so we absolutely have a duty to render that.”