Federal agents and police detectives arrested a Connecticut man, a naturalized United States citizen from Pakistan, early Tuesday in connection with the failed Times Square car bombing, according to people briefed on the investigation.

The man, Faisal Shahzad, was believed to have recently bought the 1993 Nissan Pathfinder that was found loaded with gasoline, propane, fireworks and fertilizer in the heart of Times Square, one of the people briefed on the development said.

Mr. Shahzad was taken into custody at Kennedy Airport, apparently trying to flee, one of the people said. Charges against Mr. Shahzad, who had returned recently from a trip to Pakistan, were not announced.

The authorities began focusing on him after they tracked the vehicle to its previously registered owner in Bridgeport, Conn., who had advertised it for sale on several Web sites. He paid cash, and the sale was handled without any formal paperwork.

The former owner told investigators that it appeared the buyer was of Middle Eastern or Hispanic descent, but could not recall his name. It was unclear how agents from the Joint Terrorist Task Force identified him. Federal authorities provided few details on Monday night about the arrest, the suspect or the scope of any conspiracy in the failed attack.

The authorities have been exploring whether the man or others who might have been involved in the attempted bombing had been in contact with people or groups overseas, according to federal officials.

The investigation was shifted on Monday to the control of the international terrorism branch of the Joint Terrorism Task Force, a multiagency group led by the Justice Department, according to two federal officials.

Officials cautioned that the investigation of possible international contacts did not mean there was a connection to a known terrorist group, but they said they were exploring all possibilities.

“It’s a prominent lead that they’re following, the international association,” said a senior official, who spoke on condition of anonymity to discuss a continuing investigation. “But there’s still a lot of information being gathered.”

On Monday, prior to the arrest, there was a sweeping response to the attempted attack in the tourist-packed city-within-a-city of Times Square — including an increased police presence, vehicle inspections and a touch of panic from veteran New Yorkers when a manhole fire flared five blocks from the scene of the failed bombing. Consolidated Edison blamed faulty wiring for the fire.

The recent sale of the Pathfinder began online. An advertisement that appears to be for the vehicle, which had 141,000 miles on the odometer and was listed for sale at $1,300 on at least two Web sites, emphasized that it was in good condition — “CLEAN inside and out!!” — with a recently repaired alternator and a new gas pump, distributor and front tires. “It does have some rust as you can see in the picture,” the seller allowed on NothingButCars.net, “but other than that, it runs great.” The other advertisement appeared on Craigslist.

In Bridgeport, the seller refused to answer questions. “You can’t interview her,” said an unidentified man at the woman’s two-story, white clapboard house. “She already talked to the F.B.I.”

The police earlier on Monday continued sifting through footage from 82 city cameras mounted from 34th Street to 51st Street between Avenue of the Americas and Eighth Avenue, and from untold number of business and tourist cameras.

But investigators appeared to have begun to assign less significance to a man who appeared to be in his 40s who was seen on one video, and it may well be because they were close to arresting the Connecticut man.

The man in the video was seen walking away from the area where the Pathfinder was parked and through Shubert Alley, which runs between 44th and 45th Streets. He looked over his shoulder at least twice and pulled off a shirt, revealing a red T-shirt underneath.

The New York police commissioner, Raymond W. Kelly, said investigators still wanted to speak to that man, but acknowledged that he might not be connected to the failed bombing. Paul J. Browne, the department’s top spokesman, said the police had stopped looking for additional video in the area that might have tracked the man’s movements.

“It may turn out that he was just somebody in the area, but not connected with the car bomb,” Mr. Browne said.

Before the arrest occurred, the police had said they might release footage of a man running north on Broadway at the time that a fire broke out in the Pathfinder.

Attorney General Eric H. Holder Jr. seemed optimistic in comments he made Monday morning. “I think that we have made really substantial progress,” he told reporters in Washington. “We have some good leads.”

The materials found in the Pathfinder were to be sent to the Federal Bureau of Investigation’s laboratory in Quantico, Va., for analysis, the police said. Janet Napolitano, the homeland security secretary, said on the “Today” show that it was premature to label any person or group as suspect. “Right now, every lead has to be pursued,” she said. “I caution against premature decisions one way or the other.” But the White House made clear that it considered the effort an act of terrorism, whoever its authors were. “I think anybody that has the type of material that they had in a car in Times Square, I would say that that was intended to terrorize, absolutely,” said the White House spokesman, Robert Gibbs.