Najibullah Zazi was arrested because

[28D] An Afghan immigrant to the United States has admitted plotting to use weapons of mass destruction against New York City. Najibullah Zazi was arrested last September in the state of Colorado.
    Najibullah Zazi once worked at Denver airport driving a shuttle bus. Today the 25-year-old Afghan immigrant [29D] pleaded guilty to three counts, including attempting to use a weapon of mass destruction. He told the judge he’d planned to sacrifice himself in a martyrdom operation, the target — New York City’s subway system. Zazi told the judge he had received weapons training from al-Qaeda. [30C]Zazi said he had agreed to carry out the attack as a protest against American military action in his native Afghanistan.