Rapper Tekashi69 was a star government witness at the trial of two men who were accused of being members of his former crew, the Nine Trey Gangsta Bloods, and who were ultimately convicted on racketeering conspiracy charges.

Now, federal prosecutors are repaying the favor for what they say was the “extraordinary” cooperation that Tekashi69 — who was born Daniel Hernandez and is also known as 6ix9ine — provided against his former associates.

In a memo filed late Wednesday, prosecutors asked the judge who is set to sentence Hernandez on Dec. 18 to show him leniency for assistance that they described as “both incredibly significant and extremely useful.”

Hernandez, the memo said, provided “an insider’s view of Nine Trey and a firsthand account of many acts of violence” that the government did not otherwise have. And he put himself and his family in harm’s way to do so, the memo said.

The prosecutors did not specify what sentence they believed Hernandez, 23, should receive, nor did they argue that he should be spared prison entirely.

But their lavish praise and detailed account of his cooperation suggested that they would seek a lenient sentence, if he is required to spend any time in prison at all.

As much credit as Hernandez’s cooperation won him from prosecutors, his September stint as a government witness in U.S. District Court in Manhattan led hip-hop fans and other rappers to call him a turncoat, a snitch and a fraud.

The trial put the platinum-selling Hernandez — a polarizing and combustible figure whose meteoric career was fueled in part by a viral presence on Instagram — in an unlikely role: testifying against the same gang that had enhanced his street credibility.

Over more than two days of testimony, Hernandez broke an unspoken code of silence to link the two men on trial, Anthony Ellison and Aljermiah Mack, to what he called “robberies, assaults, drugs, stuff of that nature.”

Lawyers for the two men sought to undermine Hernandez’s testimony by calling him a liar who hoped to avoid a long prison term for himself.

“You don’t think he would do whatever he needs to do to go home?” Deveraux L. Cannick, Ellison’s lawyer, told jurors during closing arguments. “There’s a motive to lie here.”

Hernandez’s lawyer, Dawn M. Florio, declined to comment Wednesday.

In the prosecution’s new court filing, the office of Geoffrey S. Berman, the U.S. attorney for the Southern District of New York, said that Hernandez had been truthful from the beginning of his cooperation, and that his information was corroborated by other evidence developed independently by the government.

Federal law enforcement authorities first approached Hernandez on Nov. 17, 2018, prosecutors said in the memo. In a meeting with prosecutors and his lawyer, he was warned of threats against him that had been intercepted on a wiretap of a cellphone belonging to a high-ranking member of the Nine Trey crew, the memo said.

Hernandez ultimately declined a government offer of protection, but he also provided some information about Nine Trey, the prosecutors wrote.

Hernandez was arrested the next day, and the following morning, he again met with prosecutors, admitting to his involvement in the gang and to his role in an armed robbery for which he had been charged, the memo said.

Hernandez provided the government with information over the course of seven sessions with prosecutors through Jan. 23, when he pleaded guilty to racketeering conspiracy and other charges, the government said. The guilty plea was initially kept secret while the investigation continued.

At the time of Hernandez’s plea, a prosecutor, Michael D. Longyear, said in court that the charges carried a sentence of at least 47 years. But Longyear added that if Hernandez cooperated successfully, the government would ask the judge, Paul A. Engelmayer, for a sentence below any minimum term.

In their memo, prosecutors said that Hernandez’s cooperation came at “great risk to his and his family’s safety, in ways far more significant than in other cases.”

They said Nine Trey was “one of the most violent sets of the United Bloods Nation, claiming members throughout the country,” and that before Hernandez’s cooperation became public, he had relocated his family.

“There is no question that the defendant’s life will never be the same because of his cooperation in this case,” the prosecutors wrote.

Based in part on his information, the prosecutors said that they were able to charge additional defendants and additional crimes.

“Hernandez provided the government with critical insight into the structure and organization of Nine Trey, identified the gang’s key players, and described acts of violence that he personally witnessed or that he heard about from other Nine Trey members,” the government wrote.

After Hernandez’s cooperation became public in February, the prosecutors added, several of his co-defendants contacted the government to begin plea discussions.

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