The head of the Minneapolis Police Department testified Monday that former officer Derek Chauvin, charged with the murder of George Floyd, “absolutely” violated department policy when he kneeled on Floyd’s neck for more than nine minutes last May 25.

Police Chief Medaria Arradondo told the court the officers who pinned Floyd to the ground until he was unresponsive should have stopped their restraint as soon as he was distressed and vocalized his discomfort.

“And clearly when Mr. Floyd was no longer responsive and motionless, to continue to apply that level of force to a person proned out, handcuffed behind their back. That … is not backed by policy, it is not backed by our training, and it’s certainly not our ethics or our values,” Arradondo said.

As rare as it is for a police officer to face a criminal trial for an on-duty killing—of which there are more than 1,000 every year—it is even more exceptional for a police chief to testify against one of his subordinates.

“It’s a pretty remarkable move on the part of the prosecution,” Dr. Cedric Alexander, the former police chief and public safety director of DeKalb County, Georgia told the Guardian. “It’s very rare that you’re going to see a chief either appear for the defense or the prosecution. But each one of these kinds of events brings its own set of circumstances. And in this particular case, where you have a knee to the neck and it’s being questioned ‘was that trained technique?’ To be able to have the chief of police … to under oath testify is clearly going to be of importance.”

Arradondo, who spoke for more than two hours, detailed the annual training officers are required to take which can include intervention training, basic CPR and first aid. He stated that officers are required to apply their medical training and skills to provide medical assistance to an individual in need while awaiting emergency medical services, which officers involved in Floyd’s death failed to do.

He later told the court that Floyd was not actively or passively resisting when officers pinned him to the pavement. Arradondo added that he was unsure if Floyd was even alive as Chauvin continued to kneel on his neck after he became unresponsive.

When prosecutors asked Arradondo about allowed uses of force, he explained that department policy allowed neck restraints at the time of Floyd’s death, but differentiated between a conscious neck restraint, meant to simply control someone, and an unconscious neck restraint, which is used to cause a person to lose consciousness. The latter was only allowed when an officer fears “great bodily harm,” Arradondo said.

Arradondo testified Chauvin appeared to be trying to employ a conscious neck restraint, which involves “light to moderate pressure” used against a person actively resisting police. However, Arradondo said what he saw in footage he reviewed of the incident constituted an unreasonable amount of force and was beyond the amount of pressure department policy allowed.

“I vehemently disagree that that’s the appropriate use of force for that situation,” he said.

Arradondo added that officers are required to be objectively reasonable in terms of their use of force and are trained to continuously assess and reevaluate a situation in the field to make sure any use of force is reasonable the entire length of time it is being applied.

When cross examining Arradondo, Defense Attorney Eric Nelson attempted to discredit him by pointing out that policy allowed officers to improvise when using neck restraints. Arradondo responded he had a “couple of issues” with the assertion that anything about Chauvin kneeling on Floyd’s neck was within policy.

Additionally, Arradondo later dismissed the defense’s argument that bystanders’ actions “distracted” officers. He stated any use of force is dependent on the “subject’s conduct, not someone else’s.” He then added that Floyd’s alleged offense, forgery, was not a crime police typically arrest someone for because it is not a violent felony, suggesting officers’ actions were entirely unnecessary.

Katie Blackwell, a superior officer and former director of the Minneapolis police training academy, also criticized Chauvin’s use of his knee to restrain Floyd.

“I don’t know what kind of improvised position that is. It’s not what we train,” she said. “What we train is one arm or two arms doing a neck restraint.”

Blackwell added that officers are trained to avoid positional asphyxia for people handcuffed and lying face down. Blackwell told jurors officers are aware that anyone in a prone position should be placed in a “side recovery position” as soon as possible

Dr. Bradford Langenfeld, the practitioner who directed Floyd’s care while he was at Hennepin County Medical Center, told jurors he spent about 30 minutes trying to resuscitate him before pronouncing him dead. Langenfeld testified he believed Floyd died from a lack of oxygen—known in medical terms as hypoxia—rather than an overdose or drug-induced heart attack.

During cross-examination, the defense focused on Floyd’s toxicology report, getting Langenfeld to agree that a combination of fentanyl and methamphetamine could cause hypoxia. Prosecutors rebuffed this by clarifying that Floyd had already been administered drugs meant to counter the effects of opioid overdoses, suggesting that any drugs in Floyd’s system were unrelated to his death.