Memphis Had Avoided Most Volatile Eruptions Over Policing. Until Now.

Dr. Adkins noted that the Police Department had in the last two years instituted a number of reforms, ranging from a ban on chokeholds to de-escalation training. “We got all these things instituted and were satisfied that had been done,” he said. “This comes as a huge shock to us that these five would perpetrate this.”

Van D. Turner, Jr., a mayoral candidate and former Shelby County commissioner who is president of Memphis’s N.A.A.C.P. branch, said he believes the city had navigated police-community relations better than many places in the years following the death of Michael Brown in Ferguson and George Floyd’s murder in Minneapolis. He noted that the majority of the nearly 2,000-strong force is Black, as is the city’s population. “It hadn’t been really bad,” he said of police-community relations. “Obviously this” — Mr. Nichols’s death — “is a strain on the relationship and I think this is something that can be healed and get better over time.”

The five officers charged with Mr. Nichols’s murder had all been hired in recent years — between 2017 and 2020.

When the city scaled back the pension plan for the police in the middle of the last decade, officers left in droves. Mark LeSure, a former Memphis police sergeant who retired in 2021, said pay cuts and other bureaucratic issues had driven many of the force’s veterans into retirement, leaving the ranks to be filled with inexperienced officers. Officers landed in specialized outfits, like the Scorpion unit, far earlier in their careers than had been typical in the past.

Adding to the potential peril is the nature of a specialized team like the Scorpion unit. It was launched after Mr. LeSure had left the force, but he had been told by former colleagues that it had a mandate to aggressively go after suspected criminals, and its members were supposed to be on the streets, doing what they could to make arrests.

“Human beings man, that’s what happened. They let their emotions get the best of them, and there was no veteran officer there to stop them,” Mr. LeSure said in a telephone interview. “Usually when vets are there, things go differently because we have that experience to say, ‘I understand you’re mad but you got to stop, you can’t do this, it isn’t right.’”

Steve Eder and Mark Walker contributed reporting. Julie Tate contributed research.