New York (CNN) -- A U.S. citizen has been arrested in the Times Square bombing probe, U.S. Attorney General Eric Holder announced early Tuesday.

Faisal Shahzad was arrested at JFK airport in New York as he prepared to board a flight to Dubai, Holder said.

"It is clear the intent behind this terrorist act was to kill Americans," Holder said. "We will not rest until we bring everyone responsible to justice."

Law enforcement officials said the suspect is the person who bought the Nissan Pathfinder used in the bombing attempt.

Earlier, a law enforcement official said the buyer is a naturalized U.S. citizen from Pakistan, and that investigators are looking at more than one person in connection with the unsuccessful bombing.

CNN has learned that the Joint Terrorism Task Force investigating the bombing attempt is considering the possibility that the attempt involved more than just a "lone wolf."

According to a source familiar with the investigation, investigators believe the plan was an intended terrorist attack to set off explosives in the heart of midtown Manhattan on Saturday night, but the individuals didn't have the expertise to detonate their device.

The Nissan Pathfinder 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. The $1,800 deal was closed at a Connecticut shopping mall, where the buyer handed over the money and drove off, the source said.

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.

A bomb made up of propane tanks, fertilizer and gasoline failed to detonate inside the SUV. New York Police Commissioner Ray Kelly said the device could have produced "a significant fireball" in the heart of Midtown Manhattan on Saturday night had it detonated properly.

Earlier, authorities said they were searching for two people they wanted to question in connection with the would-be bomb. A video obtained from a tourist in the area shows a person apparently running north on Broadway, while 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."

The question of who was behind the failed bomb attempt was the subject of intense scrutiny Monday. U.S. Attorney General Eric Holder said investigators have some "good leads," but he declined to elaborate. And Kelly said it was "too early to say" whether the attempt was carried out by a lone wolf, 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 there was no "credible evidence" at the early stages of the investigation that the Pakistani Taliban was responsible for the Times Square bomb incident.

And 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."

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.

But 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.

And Jim Cavanaugh, a former agent with the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives, 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.

The device inside the Pathfinder was made up of propane tanks, gasoline and fertilizer that turned out to be of a non-explosive grade, along with a metal pot containing wiring and firecrackers. More firecrackers were found in a can on the back seat of the vehicle, sandwiched between two full, five-gallon gasoline cans and connected by wires to clocks.

Cavanaugh 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," he 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 told CNN.

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.

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.

CNN's Deborah Feyerick, Susan Candiotti, Barbara Starr, Jeanne Meserve, Kathleen Johnston and Terry Frieden contributed to this report.