Al Qaeda Suspect Lived In Queens

The FBI has has arrested an American citizen living in Queens, NY suspected of being a member of Al Qaeda, ABC News has learned.

Mohammed Junaid Babar, of Pakistani descent, has been held as a material witness since April.

U.S. officials believe Babar was part of a terrorists plot to launch a series of bombings and assassinations in London.

Sources tell ABC News that Babar has begun cooperating with law enforcement officials. He has suggested Al Qaeda was planning more attacks in the U.S. Babar also has allegedly told investigators that Al Qaeda had developed a scheme to smuggle terrorists across the Mexican border into the United States.

"One of the things Al Qaeda does is they're constantly testing our security, whether it's at airports, whether it's at facilities, or at the border," said Jerome Hauer, Associate Director of the Center for Counterterrorism Technology and Analysis. "And I think they've found that the Mexican border is relatively easy to get people through."

The London-based terror cell Babar allegedly is associated with was under surveillance for 53 days this spring. Law enforcement officials there say the suspects spoke openly of launching attacks and had purchased nearly a ton of ammonium nitrate — one of the key ingredients used in the Oklahoma City Bombing in 1995.

"I can't imagine the repercussions of a bomb that size in downtown London, if that was the case," said Jack Cloonan, an ABC News consultant and former former FBI counterterrorism agent. "A ton of ammonium nitrate packaged in a car or lorry and delivered to a site and exploded is going to be huge, particularly in an urban environment."

British authorities alerted U.S. officials to a possible American connection to the plot — Mohammed Babar:

The FBI arrested him immediately.

"Your reaction is going to be immediate, and has to be," said Cloonan. "Because if you're linking this person on our end, the United States to this group, are we saying is there somebody else here who is planning something here."

Tonight the FBI is running down leads, trying to verify Babar's information and trying to determine if he has any associates.