But those aggressive anti-narcotics cases created a vacuum of leadership that has fueled violence and disorder on the streets, local and federal investigators said. “Therein lies the challenge of the void,” said one local law enforcement official who spoke on the condition of anonymity to discuss a continuing investigation. “Who tries to fill it? And how do we react to it?”

Federal prosecutors believed then that they had crippled the gang, but as law enforcement resources were shifted elsewhere, the Trinitarios re-emerged, said a former federal law enforcement official, who asked not to be identified because the official was not authorized to speak to the press. None of the 12 men arrested and indicted so far in Lesandro’s murder were on the Justice Department’s radar four years ago. All pleaded not guilty to murder and conspiracy charges in State Supreme Court in the Bronx on Wednesday.

“These people revitalized the gang,” the official said. “New leaders have come to the forefront.”

$5 Dues, and a Prayer

Richard Gonzalez joined the Trinitarios while serving time in prison in 2003 and later rose to become the leader in the Bronx and Manhattan for a time, before being swept up in a federal raid in 2010. Three years later, he agreed to testify in Federal District Court in Manhattan against his former friends, offering a rare insider’s account of the gang’s customs and helping to send five people to prison.

“When you become a member of the Trinitarios, if you have any outstanding debts, they are paid for,” Mr. Gonzalez testified in 2014. “If you have any problems with any individuals or any type of conflicts, they are resolved, whether it is diplomatically or with violence. These are the people that look out for you, that take care of you when you go to prison.”

One needs a sponsor to join, and once in, new members receive a rule book, take an oath and swear to abide by the gang’s constitution, Mr. Gonzalez and the federal law enforcement official said.

Members pay $5 dues at mandatory weekly chapter meetings, funds that are used for bail, weapons, parties, drugs, prison commissary costs, even everyday items like Pampers. The meetings end with a Trinitarios prayer, with the members standing in a circle, heads bowed, arms crossed, holding hands. “There really is a sense of brotherhood,” the former law enforcement official said.