Mr. Locascio is serving a life sentence. He was convicted in 1992 alongside Mr. Gotti by the same United States attorney’s office that brought last week’s indictment. Mr. Gotti, who died in prison in 2002, was found guilty of, among other things, ordering the killing of Paul Castellano in 1985, the last time a Gambino boss was gunned down in the street.

On March 14, the day after Mr. Cali’s death, Mr. Campos drove into Manhattan around 5:50 p.m. to discuss the circumstances of the murder with Gambino family members, seemingly unaware that law enforcement was tracking his every move.

He parked near a pizzeria on the Upper East Side, according to a person familiar with the matter. As the night progressed, he met with Gambino family captains on the Upper East Side and near a church in Brooklyn. They stood in the street, chatting openly, but law enforcement officials could not hear the conversations.

Several days later, Mr. Campos and Mr. Fiore drove to Staten Island for a secret meeting. A group of about eight high-level Gambino lieutenants gathered to discuss Mr. Cali’s murder, a court filing said. In a wiretapped call the next day, Mr. Fiore complained that he had stayed out past midnight.

Mr. Fiore said on the call that a woman had been at Mr. Cali’s home the night of his death, pointing to her as a possible connection. Court papers do not reveal the woman’s identity.

Nobody within the mob family seemed to suspect the person who was ultimately charged with Mr. Cali’s murder: a 25-year-old who lived with his parents on Staten Island, believed in far-right conspiracy theories and appeared to have no clear motive.