Khan moved with his family to Baltimore in 1996 but never obtained U.S. citizenship. He went to Pakistan after the Sept. 11 attacks and was introducted by his uncle and cousin, both al-Qaeda members, to Khalid Shaikh Mohammed.
Because of Khan's excellent English and knowledge of the United States, Khan was selected to conduct an attack inside the country.
He took part in plotting to blow up gas stations, poison water reservoirs and kill Pakistani President Pervez Musharraf.
In fall 2002, he delivered money to Zubair, a Jemaah Islamiyah operative, to support attacks against Western targets.