Long Island al-Qaida recruit-turned-informant Bryant Neal Vinas aided in opening or closing more than 30 terrorism investigations and his cooperation should be given “significant weight” at his upcoming sentencing, the government said in a letter to the judge partly unsealed Friday.

“He provided critical intelligence and unique insight regarding al-Qaida and its members, and his availability as a testifying witness led to numerous successful criminal prosecutions and convictions,” prosecutors told Brooklyn U.S. District Judge Nicholas Garaufis.

Vinas, 34, formerly of North Patchogue, went to Pakistan to participate in jihad in 2007. Captured and turned over to the U.S. in 2008, he pleaded guilty to aiding a rocket attack on a U.S. base in Afghanistan and providing information for a possible attack on the Long Island Rail Road.

He is scheduled to be sentenced on April 20. Federal guidelines call for him to receive 30 years to life, but Garaufis could trim that significantly based on the government’s letter. It said he may have been the “single-most valuable cooperating witness” on al-Qaida activities in 2007-2008.

Over eight years, the government said, he participated in more than 100 interviews, testifying and providing other assistance in terrorism trials, providing information on domestic threats and intelligence about al-Qaida’s means and methods, and aiding foreign governments.

The government’s letter, first filed under seal in February, was partly unsealed at the request of a journalist, but large sections with details of his cooperation remain blacked out, in some cases because investigations are still ongoing, according to prosecutors.

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Prosecutors said that since he began cooperating, Vinas has expressed no continuing interest in engaging in violence or terrorism, but they said that it was difficult to evaluate his “current mindset” because he “has become increasingly withdrawn and less willing to communicate with the government.”

“Specifically, when Vinas first began cooperating, he was engaged with law enforcement agents and volunteered relevant information,” the government said. “More recently, the government has observed that Vinas appears less engaged.”

Vinas’ lawyer, Steve Zissou, said his client is suffering the psychological effects of nearly a decade of isolation that has gone on longer than he ever expected without any final resolution.

“He’s exhausted at how long this has been, and he’s eager to know how much longer a sentence he will receive, if any,” Zissou said. “Despite the extraordinary contribution he has made he remains ready, willing and able to cooperate in whatever way the government needs him.”

Prosecutors urged the judge to include mental health treatment and vocational training, and a long term of supervised release after Vinas’ imprisonment as components of his sentence.