As five Memphis police officers attacked Tyre Nichols with their feet, fists and a baton, others milled around at the scene, even as the 29-year-old cried out in pain and then slumped limply against the side of a car.

Just like the attack on George Floyd in Minneapolis nearly three years ago, a simple intervention could have saved a life. Instead, Nichols is dead and the five officers are charged with second-degree murder and other crimes.

More disciplinary action may be coming now that the harrowing video of Nichols treatment has been released. Memphis police relieved two other officers of duty Monday and say the department is still investigating what happened. The Memphis Fire Department also fired three emergency response workers who arrived on the scene for failing to assess Nichols’ condition.

The Memphis and Minneapolis police departments are among many U.S. law enforcement agencies with “duty to intervene” policies. The Memphis protocol is clear: “Any member who directly observes another member engaged in dangerous or criminal conduct or abuse of a subject shall take reasonable action to intervene.”

It’s not just a policy, it’s the law. The three Minneapolis officers who failed to step in and stop former Officer Derek Chauvin from kneeling on Floyd’s neck as the Black man said he couldn’t breathe were all convicted of federal civil rights violations.

Experts agree peer pressure, and in some cases fear of retribution, is on the minds of officers who fail to stop colleagues from bad actions.

“They’re afraid of being ostracized,” said George Kirkham, a criminology professor emeritus at Florida State University and former police officer. “You’ve got to depend on those guys. It’s the thin blue line. When you get out there and get in a jam, you’ve got nobody else to help you but other cops.”

Nichols was pulled over in a traffic stop the night of Jan. 7. Body camera video shows he was beaten as officers screamed profanities, even as Nichols seemed confused about what he did wrong. Amid the chaos, he ran and was eventually caught at another intersection, a short distance from his mother’s house.

Security camera images from that scene show two officers holding Nichols to the ground as a third appears to kick him in the head. Later, another officer strikes Nichols repeatedly with a baton as another officer holds him.

Officers pull Nichols to his feet, though he’s barely able to stand. An officer punches him in the face, and Nichols stumbles, still held up by two officers. After more punches, he collapses. But the attack continues.

When it ends, Nichols is slumped against a car. It would be more than 20 minutes before medical attention was rendered, though three members of the fire department arrived on the scene with medical equipment within 10 minutes. Those workers, two medics and a lieutenant who was with them, were the personnel fired late Monday.

Chuck Wexler, executive director of the Police Executive Research Forum, a Washington-based think tank, said duty to intervene policies became common after officers attacked and badly injured Rodney King in Los Angeles in 1992.

“But having a policy and overcoming what many would argue is the culture in policing are two different things,” Wexler said. “It’s not enough to simply have a policy. You need to practice. You need to talk through it.”

In some cases, concerns by officers about retaliation for intervening have proven true.

In Buffalo, New York, Officer Cariol Horne was a year away from collecting her pension when she faced departmental charges after pulling a fellow officer’s arm from around the neck of a domestic violence suspect in 2006. She was fired. In 2021 a state Supreme Court judge reinstated her pension and overturned her dismissal.

Last year in Sunrise, Florida, Sgt. Christopher Pullease was criminally charged after an incident caught on video in which an unidentified female officer pulled Pullease by the belt away from a handcuffed suspect after Pullease pointed pepper spray at him. Pullease responded by putting a hand on his colleague’s throat and pushing her away, the video showed.

Experts were also perplexed that no police department supervisors were present during the Memphis incident. Had there been, they said, the outcome might have been different.

“I was a supervisor for a long time, and you showing up on the scene even unannounced keeps people from doing, for lack of a better adjective, stupid things,” said former New York City Police Sgt. Joseph Giacalone, who teaches at the John Jay College of Criminal Justice in New York.

Memphis Police Director Cerelyn “CJ” Davis said the police department has a supervisor shortage and called the lack of a supervisor at the incident “a major problem.” Davis on Saturday disbanded the city’s so-called Scorpion unit, whose officers were involved in the beating.

University of Missouri-St. Louis criminologist David Klinger said decisions on whether to intervene in a police colleague’s actions are not always cut and dried. He said one officer may see a weapon that is blocked from the view of another, for example, and stepping in at the wrong time could jeopardize the lives of officers at the scene.

“Training has to be precise about the sorts of circumstances that would warrant an intervention,” Klinger said.