Najibullah Zazi, a native of Afghanistan but a legal permanent U.S. resident living Aurora, Colo., pleaded guilty to conspiracy to use weapons of mass destruction, conspiracy to commit murder in a foreign country and providing material support to al-Qaida, the U.S. Justice Department said.
In a statement, U.S. Attorney General Eric Holder said, "This was one of the most serious terrorist threats to our nation since Sept. 11, 2001, and were it not for the combined efforts of the law enforcement and intelligence communities, it could have been devastating."
The department said Zazi faces up to life in prison on the first two counts and 15 years on the third.
As part of Monday's plea, Zazi admitted he and others went to Pakistan in August 2008 to join the Taliban in the war against U.S. and allied forces, the department said.
But instead of fighting for the Taliban, Zazi and others were recruited by al-Qaida, which trained the men in several types of weapons. The department said al-Qaida leaders asked Zazi and others to return to the United States to conduct "suicide operations."
Zazi and al-Qaida leaders discussed individual targets, including New York City subway trains, the department said.
Zazi returned to the United States in January 2009 and moved to Denver, the department said, traveling to New York later to meet with other conspirators. Returning to Denver, he bought large quantities of bomb-making materials, U.S. officials said.
Once again in New York last September, Zazi realized that law enforcement officers were investigating him, and he and others discarded their explosives, the department said. He traveled to Denver, where he was arrested by the FBI on Sept. 19.