WHEN POLICE arrived at the West Philadelphia home of Walter Wallace Jr. on Monday afternoon, it reportedly was the third time that police had gone to the address that day. Not a lot is publicly known about what happened the first two times police responded, but Mr. Wallace’s family said it was seeking help for the 27-year-old, who struggled with mental illness. Mr. Wallace was instead shot and killed by police, and the nation once again is confronted with agonizing questions about the treatment of a Black man.

A joint investigation by police and the Philadelphia District Attorney’s Office into the death of Mr. Wallace is underway. Police said officers were responding to a call about a man who was screaming and armed with a knife. Mr. Wallace, a police spokesman said, was shot after he was told to drop the knife and advanced toward police. A cellphone video taken by a bystander and widely circulated on social media shows a sequence in which Mr. Wallace is standing on a sidewalk holding a knife, two police officers are several feet away pointing their guns at him, and a woman — believed to be Mr. Wallace’s mother — seems to try to intervene. “Bro, they just killed him in front of me,” a man is heard saying amid the screams that follow shots being fired.

The president of the police union defended the officers for “doing their job and keeping the community safe, after being confronted by a man with a knife.” No doubt it was a terrifying moment, but that doesn’t mean the officers’ use of lethal force was justified or that there weren’t other options. Why was a 911 call for a mental health crisis answered with officers and drawn guns? Shouldn’t there have been attempts to de-escalate the situation? Couldn’t the officers have backed away rather than opening fire on a person in such obvious mental distress? The questions go to the heart of the debate over police use of lethal force.

A recent study by the Police Executive Research Forum concluded that many police tactics are outdated and ineffective and that lives — those of police as well as citizens — could be saved with an emphasis on de-escalation strategies. The think tank developed a new training protocol that discourages actions that can increase the anxiety of a troubled person — such as drawing a gun and shouting commands — in favor of creating distance, engaging in conversation and taking time for peaceful resolution. A recent examination of that training by the Louisville Metro Police Department found a dramatic reduction in use-of-force incidents by police as well as a decrease in injuries to officers and civilians.

As Philadelphia tries to deal with the fallout caused by Mr. Wallace’s death — there have been protests and some violence and looting that rightly have been condemned by Mr. Wallace’s grieving family — it’s important that officials take steps to improve how people in need of help get it. The de-escalation training developed by the Police Executive Research Forum would be a good place to start.

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