Minneapolis police officer Derek Chauvin was charged Friday with third-degree murder and manslaughter in the death of George Floyd. Video of Chauvin, who is white, with his knee on the neck of Floyd, who is black, has caused days of protests and rioting in the Twin Cities and other communities across the country.
According to charging documents, an autopsy showed no evidence of strangulation or "traumatic asphyxia," but it says being restrained by police, combined with Floyd's underlying health problems, likely contributed to his death.
In recent years, many police departments have trained officers to be alert to the risk of what's called "positional asphyxia," the possibility that prolonged restraint of a suspect in a prone position can be deadly. It's a lesson some in the Minneapolis Police Department already learned once, 10 years ago.
Minneapolis paid out $3 million to settle a lawsuit over the 2010 death of David Smith, 28. The young black man was mentally ill, his attorneys said, and died after officers Tasered him and then held him facedown on the floor for several minutes. One of them kept a knee on his back even after he stopped responding to questions.
This video is excerpted from evidence presented in the court proceeding. As you can see in this video at 0:13, the officer is using a similar move-- a knee in the back of a man lying face down-- as officers used with George Floyd.
The above video came from a personal camera carried by one of the officers, and was evidence in the lawsuit. The attorney for Smith's family, Bob Bennett, says the parallels between that video and the images of what happened to George Floyd are "stark."
"Both videos show an inhumanity and uncaringness that are quite frightening, I think," he says.
Bennett says when Minneapolis settled the Smith case, it pledged additional training for officers in how to restrain suspects more safely. At the time he assumed the police department would follow through with the training, but now he's not sure.
This kind of training has become more common in recent years, especially after the death of Eric Garner, who was tackled around the neck and held down by New York City police in 2014. His repeated cries of "I can't breathe" became a rallying cry for Black Lives Matter and police reform.
This week, many police on social media condemned the video of Floyd's arrest, saying they'd been trained never to knee a suspect in the neck, or maintain pressure on someone's back longer than necessary.
Jack Ryan, a retired police captain with Legal & Liability Risk Management Institute, trains officers around the country. He posted a video reminder for officers.
"We ought to have it stamped, or maybe a tattoo, on the back of our hand, that as soon as the person is subdued or restrained, then get off them.... get them into an upright position or on their side to facilitate breathing," he says in the video.
Ryan says this message has been muddied in recent years by dueling studies about whether positional asphyxia is a real threat. Some courts have accepted arguments that it's not a physiological reality, and one police academy trainer told NPR that he tells his cadets that positional asphyxia has been "debunked."
In the U.S., training and tactics are still largely defined by local departments, police academies and, to a lesser degree, state boards. The result is a patchwork of approaches to questions like this.
"Part of the problem is the lack of centralized, specific guidance," says Seth Stoughton, a former police officer who now specializes in questions of police use-of-force at the University of South Carolina Law School.
"But I don't think that's the entire problem," he said. "I think part of the problem is also a very strong cultural resistance to criticizing other cops."
Stoughton says one of the most important failures in the Minneapolis video from Monday was the fact that other officers did not intervene or even appear to say anything to Chauvin as he knelt on Floyd's neck.
Walter Katz, an expert in police reform and oversight with Arnold Ventures, says he's even more dismayed by Chauvin's indifference to the anguished complaints from bystanders.
"People were yelling at him as to what he was doing, and he continued to do so," Katz says. "To me that is not a training issue. To me that is a reflection of a culture issue."
He says questions of tactics matter less here than the officers' attitude toward the person being restrained.
"If there's a belief that some members of the community deserve less dignity than others, these types of things will keep on happening," Katz says.