After separating from Jason’s father, Ms. Reeves fell behind on a subprime mortgage and sold her house in South Florida for a loss, according to property records. She moved north, first settling in the Bronx from July 2008 through the fall of 2011, when she moved to the Albany Houses in Crown Heights.

Her son stayed behind in Florida, often running into trouble with the authorities. A review of court records showed that Mr. Reeves faced several separate felony charges of battery, burglary, domestic violence, assault, robbery with a firearm and domestic violence from 2005 through 2008. Some of his early offenses were prosecuted through a specialized mental health court in Broward County, and in 2006 he was institutionalized by the courts after being found mentally incompetent to stand trial, according to court records.

By September 2010, Mr. Reeves had moved north to the Bronx to live with his mother. He was arrested again that month, suspected of breaking and entering into a ground-floor apartment in the northeast Bronx. He and his mother moved to the Albany Houses in Brooklyn in 2011, but two years later, Mr. Reeves was arrested on suspicion of burglarizing a factory in Greenpoint.

During the past year, Mr. Reeves began to use crack openly, stopped washing and became threatening and erratic, acquaintances and neighbors said. More than once, his mother approached young men who hung out in the lobby and stairwells of her building, asking them for help with her son.

A neighbor, Asia Djones, said she heard Ms. Reeves say to the young men that if they were selling drugs, “please don’t sell my son drugs.”

Toward the end of last summer, Mr. Reeves started dropping weight and getting new tattoos. He began menacing his neighbors, they said, snatching pocketbooks, drinking openly and hustling people in the building for money.

Last year, according to neighbors, his mother sent him back to Jamaica in hopes that he would find peace. It didn’t work. Ms. Reeves told her friends that her son had been beaten within an inch of his life over drugs, leaving him with missing teeth and a newly misshapen face.