Washington (CNN) -- A former top leader of a Somali terror group, who also had ties to al Qaeda, secretly pleaded guilty in 2011 to federal charges and has provided the U.S. government with valuable intelligence information, the Justice Department said on Monday.
Ahmed Abdulkadir Warsame was a leader of al-Shabaab in Somalia and arranged a weapons deal at one time with Yemen-based al Qaeda in the Arabian Peninsula, according to court documents.
The U.S. military captured him at sea in April 2011 while he was traveling from Yemen to Somalia. He pleaded guilty in New York the following December to nine terrorism charges.
Among other things, Warsame admitted to conspiring to provide material support to al-Shabaab and al Qaeda's operation in the Arabian Peninsula, conspiracy to teach others how to make bombs, and receiving miltary-type training from a terrorist organization.
Warsame, now in his mid 20s, faces up to life in prison. A law enforcement official said he could get a lighter sentence if he "provides substantial assistance" to the United States.
"The capture of Ahmed Warsame and his lengthy interrogation for intelligence purposes, followed by his thorough questioning by law enforcement agents, was an intelligence watershed," said Preet Bharara, U.S. Attorney for the Southern District of New York.
Justice Department spokesman Dean Boyd said the United States "continues to make active use of the information" Warsame provided and his "cooperation has been and continues to be enormously valuable."
The Justice Department would not disclose specifics about Warsame's cooperation.
John Carlin, acting assistant attorney general for national security, added that Warsame was a link between terror groups and was "an operational leader, commanding hundreds of fighters."
Court papers showed that from 2007 until his capture, Warsame conspired with others, including some Americans, to provide material support to al-Shabaab and fought as a soldier for the group.
Warsame also had an extensive relationship with al Qaeda in the Arabian Peninsula, the group allegedly behind the failed Christmas 2009 bombing attempt of a Delta Air Lines jet heading to Detroit.
Court papers said Warsame brokered a weapons deal so that al-Shabaab could get arms directly from the al Qaeda affiliate in Yemen. He also conspired to provide various forms of material support, including money, training, personnel and communications equipment, to that al Qaeda branch.
Warsame also received training in how to use explosives and other weapons from al Qaeda in 2010 and 2011 and planned to train other al-Shabaab members once he returned to Somalia, documents showed.
The government gave its justification for keeping Warsame's guilty plea and cooperation secret in a March 2012 court filing.
"At this stage, any public confirmation that the defendant has pleaded guilty, in a case which attracts media attention, is likely to be widely reported and, as a result, is likely to undermine the ability for the government to further investigate and prosecute associates of the defendant and to pose a threat to the safety of his family abroad," the document said.
"Public confirmation that the defendant is cooperating on an ongoing basis could lead those associates to destroy evidence (including, for example, any e-mail messages or other communications) or to flee or otherwise change their patterns of behavior and communication," the document said.
That document also said the government was interviewing him weekly in "regular, multi-hour proffer sessions." It said his co-conspirators include "high-level, international terrorist operatives."
Lee Alan Ginsberg, a lawyer for Warsame, had no comment on the matter.