The key suspect in an alleged plot to attack New York City with homemade bombs has begun cooperating with investigators and is preparing for a possible plea deal, two law enforcement officials familiar with the investigation said Monday.

Najibullah Zazi, an Afghan immigrant, has begun talking to authorities and plans a guilty plea that could come as early as Monday, law enforcement officials told The Associated Press. They spoke on condition of anonymity because the investigation into the terror plot is ongoing.

As important as a plea would be, 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 sit-down with his attorney and federal prosecutors in Brooklyn. The sit-down, known as a proffer session, typically signals that a defendant has begun cooperating in a bid for a plea deal.

Zazi's attorney, William Stampur, didn't immediately return a telephone message Monday.

Zazi _ accused of receiving explosives training in an al-Qaida terror 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 people 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 that Zazi and others bought beauty supplies in Colorado, the western state where the former New York resident was most recently living, 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 Zazi's car after he arrived turned up bomb-making plans on a laptop computer, but no actual devices or materials.

The cooperation by Zazi suggests prosecutors hope to expand the case and bring charges against other suspects in his case and possibly other terror 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-Qaida and other terror suspects should be tried in civilian courts, federal prosecutors have sought to demonstrate that they can persuade suspects like Zazi to cooperate and provide more reliable information without coercion.

One of the people familiar with the Zazi case told the AP 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 bond and allowing him to return to his home in suburban Denver.

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

Another one of the people said that Zazi told prosecutors that he made roughly two pounds of a powerful and highly unstable explosive called triacetone triperoxide, or TATP.

Court documents indicate that Zazi and others bought acetone _ nail polish remover _ and other ingredients that can be used to make TATP. The same explosive was used by would-be shoe bomber Richard Reid in 2001 and the terrorists who carried out the London bombings in 2005 that killed 52 people.

In those instances, TATP was not the main charge; it was the detonator. The 1.5 grams in Reid's show was supposed to help detonate the plastic explosives aboard a jetliner, and it was used to set off a mixture of black pepper and hydrogen peroxide in London.

Experts has said the TATP in the Zazi case was most likely going to be just the detonator.

But in each of those earlier instances, TATP was not the main charge _ it was the detonator. It was supposed to help detonate the plastic explosives in Reid's shoe aboard a jetliner, and it was used to set off a mixture of black pepper and hydrogen peroxide in London.

The FBI's New York office and the U.S. attorney's office in Brooklyn declined comment on Monday.

Authorities say Ahmedzay and another New Yorker charged in the case, Adis Medunjanin, traveled to Pakistan with Zazi in 2008. Medunjanin has pleaded not guilty to charges he conspired to kill U.S. soldiers in Afghanistan and remains jailed.

The three men, former high school classmates in New York, are scheduled to appear in federal court in Brooklyn on Feb. 25.

Officials earlier confirmed reports week that Zazi's uncle had been arraigned on a felony count in secret _ a sign that he also could be cooperating.

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Associated Press writer Devlin Barrett in Washington contributed to this report.