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Najibullah Zazi, seen here in Denver on Sept 17, 2009, was arrested for his alleged role in a plot to launch an attack in New York City using homemade explosives. ((Ed Andrieski/Associated Press))

The key suspect in an alleged plot to attack New York City with homemade bombs has pleaded guilty to conspiracy to use weapons of mass destruction.

Najibullah Zazi, a 25-year-old Afghan immigrant, also pleaded guilty on Monday in New York City to counts of conspiracy to commit murder in a foreign country and providing material support for a terrorist organization.

He faces a life prison sentence without parole in the plea deal.

As important as a plea is, Zazi may be far more valuable to investigators as a source for information about co-conspirators in the United States and Pakistan.

Three people with inside knowledge of the investigation confirmed that the jailed Zazi volunteered information during a recent meeting with his attorney and federal prosecutors in Brooklyn. The sit-down, known as a proffer session, typically signals that a defendant has begun co-operating in a bid for a plea deal.

Zazi — accused of receiving explosives training in an al-Qaeda terrorism camp in Pakistan — told prosecutors that he was armed with bomb-making components while en route to New York City last year, but got rid of them along the way, the sources said.

Zazi's account, if true, could explain what happened to explosive materials authorities suspect were meant for a possible attack on the New York City transit system.

The government alleges the airport driver and others bought beauty supplies in Colorado to make peroxide-based bombs before he tried to mix the explosives in a hotel room there and then set out cross-country by car in September. Searches of his car after he arrived turned up bomb-making plans on a laptop computer, but no actual devices or materials.

Co-operation could aid other terrorism probes

The co-operation by Zazi suggests prosecutors hope to expand the case and bring charges against other suspects and result in other terrorism probes. At the time of Zazi's arrest, Attorney General Eric Holder called the case the most serious terrorism threat since the Sept. 11, 2001, attacks.

Amid the debate over whether alleged al-Qaeda and other terrorism suspects should be tried in civilian courts, federal prosecutors have sought to demonstrate that they can persuade suspects like Zazi to co-operate and provide reliable information without coercion.

One of the people familiar with the Zazi case told The Associated Press that Zazi decided to offer the information after being warned that his mother could face criminal immigration charges.

Zazi's father was charged earlier this month with trying to get rid of chemicals and other evidence. But it appears he was cut a break: After initially demanding that he be jailed in Brooklyn without bail, prosecutors agreed to a deal on Feb. 17 releasing him on $50,000 US bond and allowing him to return to his home in suburban Denver.

By contrast, bond for a Queens imam charged with lying to the FBI about phone contact with Zazi when Zazi was in New York was set at $1.5 million US. One of Zazi's friends, New York cab driver Zarein Ahemdzay, was jailed without bail on a similar charge of lying.

One of the sources said that Zazi told prosecutors he made close to one kilogram of a powerful and highly unstable explosive called triacetone triperoxide, or TATP.