Court papers unsealed in federal court in Brooklyn 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 Wednesday, and no court appearances were scheduled. But a law enforcement official, speaking on condition of anonymity because the official was not authorized 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.
The official described Vinas as a militant convert who was captured last year in Pakistan.
Prosecutors charged Vinas in a rocket attack on U.S. forces in Afghanistan in September 2008. Court papers allege he also gave "expert advice and assistance ... on the New York transit system and Long Island Railroad."
The Metropolitan Transportation Authority said in a statement Wednesday that there was never an imminent threat to the system.
"As part of the Joint Terrorism Task Force, the MTA has been in constant communication with local and federal authorities as the investigation involving Bryant Neal Vinas developed," the statement said.
People familiar with the case say Vinas told counterterrorism investigators that he met senior al-Qaida members while staying at a network of hideouts on the Afghanistan-Pakistan border, where he trained from about March 2008 to August 2008.
Vinas named several of the terror group's officials and described their activities, including rocket and mortar strikes against U.S. forces in the area, said the people, who spoke Wednesday on condition of anonymity because they weren't authorized to disclose details of his statements. Vinas also revealed discussions among terrorists about potential civilian targets in Europe and described training in weapons and explosives, they said.
Vinas received "military-style training" from al-Qaida, according to court papers.
Also, a defense attorney in a terrorism case in Belgium said prosecutors there traveled to New York earlier this year to interview Vinas. The lawyer, Christophe Marchand, said Vinas had provided a statement against the French and Belgium defendants charged with going to Pakistan to volunteer to fight with al-Qaida.
Marchand denied his client was a terrorist or knew Vinas.
"He never talked about meeting an American - never," the lawyer said.
Vinas' attorney, Len Kamdang, wouldn't comment, other than requesting "the public withhold judgment in this case until all of the facts become available."
A woman who answered a family phone number found in public records said she was the Vinas' mother and had not seen her son since he moved out 10 years ago at age 18.
"He's a stranger to me," she said before hanging up without giving her name.
There was no answer at the door at a family address, a two-story home with a manicured lawn and landscaping on a cul-de-sac in Patchogue, about 55 miles east of Manhattan.
Vinas' Peruvian-born father, Juan Vinas, told Newsday in a recent interview that federal agents had interviewed him. He said he didn't know where his son was.
"The FBI asked me all kinds of questions about him, but they don't tell me nothing," he said.
The president of the Islamic Association of Long Island, a mosque in nearby Selden, said he recalled a "very quiet, polite, smiley" young Hispanic man called Ibrahim, who was a frequent but unassuming presence at the mosque for about a year, starting roughly 2 1/2 years ago.
He turned up four to five times a week for services but never participated in any social activities at the mosque, said president Nayyar Imam. He said Ibrahim apparently converted to Islam and changed his name before he began coming to the mosque.
"He's the last person in the mosque you would think about" getting involved in terrorism, Imam said.
In sealing the courtroom for the January guilty plea, a judge said that a public plea could harm a confidential investigation involving national security.
The Vinas case is a rare instance of an American al-Qaida recruit cooperating with Western authorities.
In 2004, Mohammed Junaid Babar, of Queens, admitted that he had traveled to the province of Waziristan to supply cash and military equipment to the terror network. Babar, who hasn't been sentenced, became a witness against three British Muslims eventually cleared of charges they scouted out potential targets on behalf of suicide bombers who killed 52 commuters on London's transit system in 2005.
NEW YORK AND TRI-STATE AREA NEWS