The flight had begun to taxi for takeoff when FBI agents ordered it to return to the gate where Shahzad and two others were taken into custody. The other two were later released, authorities said.
Authorities said they found a 9 mm handgun in Shahzad's car and two loaded ammunition magazines.
Shahzad was questioned for several hours by the FBI agents and, according to WABC-TV, said he had acted alone in carrying out his attempted bomb plot in Times Square.
Shahzad is a naturalized American citizen, who had recently returned from a five-month trip to Pakistan and the city of Peshawar, a known jumping off point for al Qaeda and Taliban recruits.
At a press conference early Monday morning, Attorney General Eric Holder said, "It's clear that the intent behind this terrorist act was to kill Americans." He urged America to "remain vigilant."
Federal authorities told ABC News that they tracked Shahzad over the last two days using evidence found in the Nissan Pathfinder left at the scene and in the unexploded bomb components.
According to authorities, Shahzad bought the vehicle on April 24, one week before the bombing attempt, through an Internet ad placed by a Connecticut family.
Members of the family told the FBI that Shahzad paid $1,300 for the vehicle in $100 bills after taking the Pathfinder on a test drive in the parking lot of a Bridgeport shopping center. FBI agents recovered a shopping center surveillance tape that they say shows Shahzad driving the car, authorities said.
He later had the windows on the car tinted, officials said, prior to driving it to New York City last Saturday.
Federal law enforcement officials said at least three other people close to Shahzad were also under scrutiny in connection with the case.
One Monday, ABC News reported that there is growing evidence the bomber did not act alone and had ties to radical elements overseas, with one senior official telling ABC News there are several individuals believed to be connected with the bombing.
Officials declined to provide the specifics that led them to believe there were overseas links to a larger plot.
Authorities said a clue in the investigation was a video posted online early Sunday morning by persons in Connecticut, who may have been involved in the bomb attempt. The video, posted on a site registered one day before the attack, has the Taliban in Pakistan claiming responsibility for the attempted bombing.
Though a Taliban leader thought killed in a U.S. drone strike resurfaced in the video threatening attacks on U.S. cities, and the Taliban has claimed credit for the failed New York attack, U.S. authorities are skeptical.
The would-be bomber packed the car with more than 100 pounds of fertilizer, but not the kind that would explode, police said.
Had the bomber chosen the right kind of fertilizer, the bomb would have had the force of more than 100 pounds of TNT. But instead of ammonium nitrate, the kind of fertilizer used by Oklahoma City bomber Timothy McVeigh, the bomber used a harmless fertilizer, New York City Police Department spokesman Paul Browne said.
The license plate on the car was apparently stolen from an auto repair shop outside Bridgeport, Conn., according to law enforcement officials.