Officer Derek Chauvin, who has since been shot, reportedly breached department policy by pushing his knee against George Floyd's neck and holding him down after Floyd had stopped fighting and was in pain, according to the Minneapolis police chief.

On Day Six of Chauvin's murder trial, Police Chief Medaria Arradondo said that continuing to kneel on Floyd's neck after he was bound behind his back and lying on his stomach was "in no way, shape or form" part of department policy or training, "and it is definitely not part of our ethics or principles."

The day after Floyd's death in May, Arradondo, the city's first Black mayor, shot Chauvin and three other officers, calling it "murder" in June.

Though police have long been accused of closing ranks to shield fellow officers accused of misconduct – the so-called "blue wall of silence" – some of the Minneapolis department's most senior officers have spoken out against Chauvin's treatment of Floyd.

Arradondo testified not only that Chauvin, a 19-year veteran of the force, should have let Floyd up sooner, but also that the pressure on Floyd's neck did not appear to be light to moderate, as required by the department's neck-restraint policy; that Chauvin failed in his duty to provide first aid before the ambulance arrived; and that he violated the department's neck-restraint policy.

The police chief said, "The action is not de-escalation." "And when we speak about the framework of our sanctity of life, when we talk about our beliefs and values, the behavior contradicts everything we're talking about."

After the emergency room doctor who pronounced Floyd dead said at the time that Floyd's heart most likely stopped due to a lack of oxygen, Arradondo testified.

Dr. Bradford Langenfeld, a senior resident on duty at Hennepin County Medical Center that night who attempted to resuscitate Floyd, testified as prosecutors tried to prove Chauvin's knee on the Black man's neck killed him.

Floyd's heart had stopped by the time he arrived at the hospital, according to Langenfeld. The doctor said he was not aware of any attempts to resuscitate Floyd at the scene by bystanders or police, but that paramedics advised him they had attempted for around 30 minutes and that he tried for another 30 minutes.

During questioning by investigators, Langenfeld said that based on the knowledge he had, asphyxia, or a lack of oxygen, was "more likely than the other possibilities" that Floyd's cardiac arrest - the stopping of his heart - was triggered by.

In Floyd's death on May 25, Chauvin, 45, is charged with murder and manslaughter. Outside a corner store where Floyd had been arrested on suspicion of attempting to pass a bogus $20 bill for a pack of cigarettes, the white cop is accused of grinding his knee into the 46-year-old man's neck for 9 minutes, 29 seconds.

Floyd's treatment by police was captured on widely circulated bystander footage, sparking nationwide demonstrations that turned violent in some cases.

The defense has argued that Chauvin did what he was taught to do and that Floyd's death was triggered by his use of illicit substances and underlying health issues.

Chauvin's lawyer, Nelson, asked Langenfeld whether any medications can induce hypoxia or a lack of oxygen. Fentanyl and methamphetamine, both of which were detected in Floyd's body, may do this, according to the doctor.

Floyd's death was eventually ruled a suicide by the county medical examiner's office, meaning it was caused by someone else.

Floyd died of "cardiopulmonary arrest, complicating law enforcement subdual, detention, and neck compression," according to the study. Fentanyl intoxication and recent methamphetamine use were classified as "other serious conditions" but not as "cause of death" in a summary study.

Although some people may become more violent while under the influence of drugs or alcohol, others may become "more vulnerable," according to prosecutor Steve Schleicher. Arradondo agreed and recognized that when officers decide to use force, this must also be considered.

Floyd fought police who were trying to place him in a patrol car, claiming he was claustrophobic, before being held to the ground.

Officers are qualified in basic first aid, including chest compressions, according to Arradondo, and department policy mandates that they seek medical help and provide necessary assistance as soon as possible before paramedics arrive.

He said, "We completely have a responsibility to make that."

Even after Floyd became unresponsive, officers continued to restrain him with Chauvin kneeling on his stomach, another kneeling on his back, and a third holding his feet before the ambulance arrived, according to testimony and video evidence.

An off-duty Minneapolis firefighter who tried to administer assistance or advise police how to do it was also turned down by the officers.

Langenfeld testified that for every minute that CPR is not provided to people who are in cardiac arrest, their chances of survival drop by 10% to 15%.

On cross-examination, Nelson said that department policies guide officers to do what is fair under the circumstances. He inquired if officers should consider the conduct of a crowd, and Arradondo agreed. Onlookers, many of whom were shouting at Chauvin, may have influenced officers' reactions, according to Nelson.

Nelson also questioned whether Chauvin's knee was on Floyd's neck, showing a few seconds of bystander video next to footage from an officer's body camera that appeared to show Chauvin's knee on Floyd's shoulder blade, which Arradondo confirmed appeared to show Chauvin's knee on Floyd's shoulder blade.

However, prosecutors immediately persuaded Arradondo to point out that the video played by Nelson only showed a few seconds before Floyd was placed on a stretcher.

Minneapolis cops are on the case. Inspector Katie Blackwell, the training division's commander at the time of Floyd's death, also testified on Monday.

She says Chauvin, whom she has known for about 20 years, received annual instruction in defensive techniques and the use of force, and that he would have been taught to restrain a person's neck with one or two arms rather than his knee.

After seeing a picture of Chauvin with his knee on Floyd's neck, she said, "I don't know what kind of improvised pose that is."

Chauvin was also a field-training officer, according to her, undergoing extra training so he could understand what prospective officers were studying in the academy.

Soon after Floyd's death, the city passed legislation prohibiting police chokeholds and neck restraints. Several policy reforms were also introduced by Arradondo and Mayor Jacob Frey, including increased monitoring of use-of-force incidents and efforts to de-escalate situations.