The Wall Street Journal reported Tuesday that he told interrogators he received training in bomb making during a recent five-month trip to Pakistan, according to a senior U.S. official familiar with the matter.
The official said received his training in the tribal region of Waziristan bordering the Afghan border, the Journal reported.
Authorities tracked down Shahzad using the vehicle identification number on the Nissan Pathfinder that failed to detonate. They linked that number to a recent sale in Connecticut, Holder said.
Once they identified Shahzad, authorities placed him on a federal air travel no-fly list. He was arrested late Monday night aboard a plane bound for the United Arab Emirates.
U.S. government officials, speaking on condition of anonymity, said Shahzad made his flight reservation on the way to the airport and paid for his ticket in cash.
New York City Mayor Michael Bloomberg, while refusing to criticize agencies, said the suspect was "clearly on the plane and shouldn't have been." An FBI official said Shahzad was placed on No Fly list hours before his arrest.
Homeland Security Secretary Janet Napolitano declined to say how Shahzad was able to board the flight if he was on the No Fly list.