New York (CNN) -- The buyer of the sport-utility vehicle used in a failed attempt to set off a car bomb in New York's Times Square is considered a potential suspect in the case, a law enforcement source said Monday.

The buyer is a naturalized U.S. citizen from Pakistan, but investigators are looking at more than one person in connection with the unsuccessful bombing, the source said.

A bomb made of propane tanks, fertilizer and gasoline failed to detonate inside the Nissan Pathfinder, which had been left in the heart of Midtown Manhattan on Saturday night. The vehicle had been sold three weeks ago in a cash deal with no paperwork exchanged, a law enforcement source with knowledge of the investigation told CNN earlier Monday.

A seller in Connecticut put the Nissan Pathfinder up for sale through the online classified ad site Craigslist and sold it to a buyer who paid $1,800 for the vehicle, the source told CNN.

The registered owner is not a suspect in the bombing attempt, New York Police Commissioner Ray Kelly said Monday. The seller described the buyer as a man in his late 20s to early 30s, and investigators are checking into phone records between the two, the source said.

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A video obtained from a tourist in the area shows a person apparently running north on Broadway. Another video shows a balding man with dark hair removing a shirt and putting it in a bag before walking out of view of the camera, which was inside a restaurant.

"These are not suspects," Kelly said. "These are people we would like to speak to."

Investigators are examining phone records of businesses that sell some of the bomb's components and chasing leads in "several locations" on the East Coast and beyond, a federal law enforcement official told CNN. The official would not say whether any of the leads were in other countries, and cautioned that the investigation could take "a few more days or weeks."

New York police have been examining the device for clues such as fingerprints, hair and fibers since Saturday. The vehicle and bomb components were taken to the FBI's forensic laboratory in Quantico, Virginia, on Monday, FBI spokesman Richard Kolko said Monday evening.

Kevin Barry, a former New York bomb squad member, said the device had "no known signature" -- a style of construction that might link it to known terrorist groups. That suggests it was the work of either an individual or a new organization, said Barry, who is now an adviser to the International Association of Bomb Technicians and Investigators.

Barry said the detonating mechanism lacked the energy needed to properly set off the explosion. Jim Cavanaugh, a former agent with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, called the bomb "a Rube Goldberg contraption" that would have been difficult to set off.

"That does not mean that the bomb's not deadly," Cavanaugh said. Someone close by could be hurt or killed. "But it's not a very reliable working system, a fusing and firing system, at all," he said.

The question of who was behind the failed bomb attempt was the subject of scrutiny Monday.

U.S. Attorney General Eric Holder said investigators have some good leads, but he declined to elaborate. Kelly said it was too early to say whether the attempt was carried out by a lone person, international terrorists, or any other type of network.

Pakistani Taliban leader Hakimullah Mehsud appeared on a video released less than 24 hours after the attempt, claiming Taliban fighters were prepared to inflict "extremely painful blows" in major U.S. cities. But a senior U.S. military official said Monday there is no credible evidence at the early stages of the investigation that the Pakistani Taliban was responsible for the Times Square incident.

Another U.S. official with direct awareness of the latest U.S. understanding of the incident said the Pakistani group has never shown "trans-national capabilities" like other groups, such as al Qaeda. But such a possibility is "not something one can rule out at this early stage," said the official, who spoke on condition of anonymity because of the sensitivity of the information.

Pakistan's Taliban movement has been linked to a 2008 plot to blow up subway stations in the Spanish city of Barcelona, and at least two of the 11 men convicted in the plot came to Barcelona from Pakistan, Spanish prosecutors said.

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One counterintelligence official told CNN there was no evidence of any communications among terrorist organizations overseas about the device after Saturday night's attempt.

"People overseas were not giving high fives ... or saying anything about the bomb not working," the official said. "There is no indication that there was that kind of tie."

Cavanaugh said the bomber could have been "internationally inspired," but the device showed little sign that a group like al Qaeda was behind it.

"Their bombs would be better funded, better fused, better materials, better knowledge," he said.

- CNN's Deborah Feyerick, Susan Candiotti, Barbara Starr and Terry Frieden contributed to this report