After that, the relationship between 6ix9ine and his street mentor deteriorated quickly. In an interview with “The Breakfast Club” days before his arrest, 6ix9ine said he had fired everyone except Mr. Grainge and attributed the split mostly to money: He had booked a national tour, but did not feel he was getting his rightful share. He also invoked the July robbery.

“I knew how strong my team was — nobody could touch me,” he said. “The only way you could touch me is if you were already next to me.”

The next day, 6ix9ine appeared via live video on Instagram and declared, “[Expletive] Treyway.” Later that afternoon, Shotti posted a video to his own account, smirking in two Treyway chains and listening to 6ix9ine’s music. He mouthed along as the rapper shouted out the crew he had just disowned: “Treyway!”

Offline, 6ix9ine was meeting with F.B.I. agents, who had picked up on wiretaps that his former crew wanted to “super violate” him for his disrespect, an expression authorities took as a threat to the rapper’s life, his lawyer said. They offered him round-the-clock protection against Shotti and his associates, but 6ix9ine declined.

By Monday, they were all in federal custody. This week, prosecutors said they had obtained a warrant for the same Instagram account that brought Mr. Hernandez to prominence, calling it “quite voluminous.”

For now, his future remains uncertain. Even if Mr. Hernandez finds leniency in the racketeering case, a conviction would likely be a violation of his probationary terms, which could lead to jail time. His supporters worry about his safety behind bars.

6ix9ine’s second album, “Dummy Boy,” initially postponed in the wake of his arrest, was released Tuesday after it leaked online. But the rapper will not be around to celebrate its likely success.

“You can’t come into the rap game and then turn around and decide you want to be a gangster,” said Charlamagne, one of the many fans, potential mentors, media personalities and industry hands who tried to guide 6ix9ine toward safer ground. “You get to a certain point, and you’ve either got to evolve or die.”