A person familiar with the case said Wednesday that during more than two weeks of questioning, the Pakistani-American also expressed surprise that the device - a mishmash of fireworks, gasoline canisters, propane tanks and fertilizer - did not detonate. The suspect said he thought the fireworks would trigger a chain-reaction that would rupture the tanks and create a deadly fireball, the person said.
Shahzad, who authorities say has claimed he received explosives training in Pakistan, even asked interrogators to explain why the device failed.
Shahzad left the vehicle on West 45th Street on a spring Saturday evening amid hundreds of people enjoying the tourist haven, prosecutors said. The attempted bombing prompted a massive police response, but no one was hurt.
Experts said the bomb had been poorly constructed with a nest of wires, battery-operated alarm clocks and heavy bags of fertilizer that couldn't explode.
There was no immediate response Wednesday to a phone message left with Shahzad's attorney.
On Tuesday, Shahzad appeared in a U.S. court for the first time since his May 3 arrest. Prosecutors had refused to disclose his whereabouts prior to the hearing, but a third official told the AP on Wednesday that he had been under guard at a Brooklyn hotel while he voluntarily answered investigators' questions.
All three people spoke to the AP on condition of anonymity because of the investigation had not been completed.
Shahzad, 30, was ordered held without bail on five felony charges including attempted use of weapons of mass destruction and attempted acts of terrorism transcending national boundaries, each of which carry potential penalties of life in prison.
The ex-budget analyst from Bridgeport, Conn., was captured while attempting to flee in a Dubai-bound plane at John F. Kennedy International Airport.
Since his arrest, Shahzad "has provided valuable intelligence from which further investigative action has been taken," the U.S. attorney's office in Manhattan said in a statement Tuesday.