Faisal Shahzad, now in custody on terrorism and weapons charges, drove a 1993 Nissan Pathfinder to New York City's landmark Times Square from Connecticut on April 28, apparently to figure out where would be the best place to leave it later, the official said. He then returned April 30 to drop off a black Isuzu, according to the source, who spoke on condition of anonymity because of the sensitive nature of the investigation.
The official told AP Shahzad went back Saturday and left the SUV loaded with firecrackers, gasoline and propane, enough to likely create a fireball and kill nearby tourists and Broadway theatergoers had it gone off successfully.
Shahzad left his Izuzu SUV on 38th Street as his getaway car, but on Saturday night - after he left the Pathfinder - he became frazzled because he had left the keys in what was then a smoking car. So he took the train home to get his keys and returned Sunday to get the Izuzu, reports CBS News Justice correspondent Bob Orr.
Shahzad, 30, admitted to rigging the Pathfinder with a crude bomb based on explosives training he received in Pakistan, authorities say. He was pulled off a plane Monday headed for Dubai and has been cooperating with investigators. For a second day Wednesday, he had yet to appear in Manhattan federal court.
Kifyat Ali, a cousin of Shahzad's father, has called the arrest "a conspiracy."
Shahzad is believed to have been working alone when he began preparing the attack, almost immediately after returning in February from his native country, authorities said. They said they have yet to find a wider link to extremist groups or to pin down a motive.
"It appears from some of his other activities that March is when he decided to put this plan in motion," New York police Commissioner Raymond Kelly said Wednesday. "He came back from Pakistan Feb. 3, 2010. It may well have been an indicator of putting something catastrophic in motion."
In leaving Times Square on Saturday, he discovered he left a chain of 20 keys including those to the getaway car and his home in Connecticut in the SUV, and had to take public transit, the official told the AP.
Investigators had already started searching for suspects, when he returned to the scene on Sunday with a second set of keys to pick up the Isuzu, parked about eight blocks from the car bomb site, the official said.
Kelly told a Senate panel that Shahzad bought a gun in March that was found in his Isuzu at Kennedy Airport, suggesting that he was moving ahead on the bombing plot shortly after returning from Pakistan.
Pakistan Ambassador Husain Haqqani said Wednesday that an investigation into Shahzad's links to Pakistan was ongoing. He said an unspecified number of people had been questioned but no one has been arrested or detained in Pakistan. Haqqani spoke to the AP prior to an appearance at Harvard University in Massachusetts.
Asked if any connection had emerged between Shahzad and Qari Hussain Mehsud, the Pakistani Taliban's chief bomb maker who is also in charge of recruiting suicide bombers, Haqqani said "no such fact had emerged," at this point in the investigation.
"I think it's premature to start identifying groups and individuals with whom he might have trained," he said.
Haqqani added that it was unlikely that Shahzad or anyone could find a bombmaking facility in the south Waziristan region because that region is now controlled by the Pakistani Army. Shahzad said he was trained in the region, authorities say.
U.S. officials have also been unable to verify whether Shahzad trained to make bombs at a terrorist camp in Pakistan.
Shahzad had previously lived in Shelton, Connecticut, but got a low-rent apartment in nearby Bridgeport when he returned from Pakistan. His wife and children apparently did not return with him.
Timeline of Times Square Bomb Plot:
Police recovered surveillance video of Shahzad at Times Square moments after the attack, and he's seen in other video in Pennsylvania buying fireworks. Neither videotape has been released.
Interviews Wednesday with business owners and police shed light on purchases Shahzad made of fireworks and a rifle.
On March 8, Shahzad bought six to eight boxes each containing 36 Silver Salute M88 fireworks from Phantom Fireworks in Matamoras, Pennsylvania, said store vice president William Wiemer. Even if used together, the fireworks couldn't have caused a large explosion, Wiemer said.
"The M88 he used wouldn't damage a watermelon. Thank goodness he used that," said Bruce Zoldan, the company's president.
Each M88 has an amount of pyrotechnic powder that is less than 1/6 the size of an aspirin, the company said. Fireworks purchased illegally can be up to 1,000 times more powerful, they said.
"There's no doubt, had he bought this on the black market, that the outcome in New York would have been totally different," Zoldan said.
Shelton police said Shahzad legally bought a Kel-Tech rifle from a dealer after passing a criminal background check and a 14-day waiting period. The owner of the gun shop declined comment.
More coverage of the Times Square Bomb Plot:
Authorities Lost Faisal Shahzad in Traffic
Shahzad: Number Cruncher to Terror Suspect
Bomb Suspect Shahzad Seen Walking Away in Video
How You End Up on the U.S. No-Fly List
Shahzad Bought Weak Fireworks, Store Owner Says