An American man charged with giving al-Qaeda information on the New York transit system and attacking a U.S. military base in Afghanistan has been a secret witness in the fight against terror both here and overseas, authorities have revealed. Court papers unsealed in federal court in Brooklyn on Wednesday identified the defendant as Bryant Neal Vinas, nicknamed "Ibrahim" or "Bashir al-Ameriki", who grew up on Long Island. His identity had been kept secret since his indictment late last year. Court papers show he pleaded guilty in January in a sealed courtroom in Brooklyn and remains in U.S. custody in New York. Federal prosecutors refused to discuss Vinas' background on Wednesday, and no court appearances were scheduled. But a law enforcement official, speaking on condition of anonymity because the official was not authorised to discuss the case, said Vinas provided critical information that led to a security alert about the New York City subway system last year. Authorities issued an alert around Thanksgiving last year saying the FBI had received a "plausible but unsubstantiated" report that al-Qaida terrorists in late September may have discussed attacking the subway system around the holidays. The origin of that report, the official said, was Vinas.