ALBUQUERQUE, N.M. — The Albuquerque Police Department was already the subject of a Department of Justice investigation when officers on March 16 shot and killed James Boyd, a homeless, mentally ill man found camping in the foothills of the Sandia Mountains.

But it was one officer’s helmet camera recording of the four-hour standoff’s denouement — Boyd agreeing to leave with the officers and collecting his belongings, then being shot as police suddenly launched an offensive — that quickly brought the city’s simmering anxiety to a rolling boil of protests and demands for change.

Boyd’s death was one of 37 officer-involved shootings, 23 of them fatal, that prompted the DOJ in 2012 to launch an investigation that culminated last week with a finding that the Albuquerque Police Department was engaged in a “pattern or practice of use of excessive force, including deadly force” that violated citizens’ constitutional rights, according to a DOJ letter to Mayor Richard Berry.

Federal investigators also found that although APD rules required officers to use the body cameras, officers often neglected to use them and were rarely reprimanded for failing to record.

Police officials say recordings most often exonerate officers and can help with investigations, but as law enforcement agencies from New York to Los Angeles increasingly adopt the cameras, the video of one man’s death in Albuquerque highlights the power of recording as a reform tool and focuses debate on how, exactly, the cameras are used.

Federal investigators reviewed 20 officer-involved shootings and more than 200 use-of-force reports from the APD and released their findings in the 46-page letter to Berry, which cited “insufficient oversight, inadequate training and ineffective policies.” The report praised the APD for adopting technologies such as lapel cameras to increase accountability but said police leaders “reacted hastily” in requiring all officers to use lapel cameras without working to earn officers’ support and then failing to make sure officers actually used them.

In fact, enforcement was so lax, the decision to require the cameras “appeared directed only at placating public criticism,” according to the report.