The videos, which are widely available on the Internet, show Mr. Boyd saying he’s afraid the officers are going to shoot him. As he picks up his bags, they shoot stun grenades and sic police dogs on him. He draws knives, presumably to defend himself from the dogs, and turns away as if to flee. Then the officers open fire with assault rifles.

Defenders of the Albuquerque Police Department pointed out Mr. Boyd’s history of mental illness and noted that early in the encounter he had threatened to kill the officers. (“I’m almost going to kill you right now,” he said. “Don’t give me another directive. Don’t attempt to give me, the Department of Defense, another directive.”) But it’s hard to watch the video and see anything but sanctioned murder.

A few weeks later, an officer with a history of being accused of using excessive force shot and killed 19-year-old Mary Hawkes, claiming she had pointed a gun at him. His lapel camera yielded no video; after analyzing the device, the manufacturer said it had either malfunctioned or been shut off. She later tested positive for methamphetamine. Less than two weeks after that, officers shot and killed a military veteran with a history of mental health issues and a gun who had barricaded himself in his home. The department later released only a brief segment of video.

Protests erupted in response to the killings, including one I watched from my front porch that shut down Central Avenue for hours, spilled onto Interstate 25 and ended in the early morning, when police shot tear gas into the streets of downtown. Protesters later disrupted a City Council meeting.

At first it seemed as if the rest of the country didn’t much care that a metro area of nearly a million people had become a powder keg. But in the two weeks since the brutal beating by the teenagers, people have started paying attention. They are asking how something that terrible could happen, what kind of place breeds violence like that. The teenagers reportedly confessed to randomly beating dozens of other homeless people in the last year. A police department spokesman, Simon Drobik, has been quoted expressing his horror and lamenting the fact that the police received no reports of the other attacks.