Federal authorities have identified a person of interest in Saturday night's Times Square bomb attempt -- a naturalized American citizen who was in Pakistan for several months and returned to the United States recently, investigative sources told Fox News.
The latest developments seem to support investigators' suspicions that there was a foreign connection behind the failed car bomb attempt in New York City, senior Obama administration officials told Fox News, shedding light on the growing body of evidence.
Sources say that evidence includes international phone calls made by the person of interest, who has not been identified publicly. The Associated Press identified the person as a man of Pakistani descent, citing unnamed law enforcement sources.
Police also have interviewed the registered owner of the bomb-laden sports-utility vehicle. They say he is not a suspect, but he recently sold the dark-colored 1993 Nissan Pathfinder on Craigslist to another individual, whom the Associated Press reports was the Pakistani-American.
The bomb scare forced the evacuation of Times Square on a busy Saturday night, as police used a robot to break into the smoking SUV and diffuse the makeshift explosive, which was made from everyday items, such as propane tanks and firecrackers.
One Obama administration official, while acknowledging the crudeness of the bomb, cautioned, "Do not necessarily assume that the plot behind it was not sophisticated."
The SUV's vehicle identification number had been removed from Pathfinder's dashboard, but it was stamped on the engine and axle, and investigators used it to find the owner of record. CBS News reports that owner told investigators he recently sold the vehicle for $1,300 to someone who looked "Middle Eastern" or "Hispanic." The buyer reportedly paid in $100 bills.
Sources told Fox News that investigators are focusing on the similarities between the failed attack in New York City and both the 2007 attack on Glasgow's airport in Scotland and the attempted bombing of a London nightclub the same year. Propane gas and gasoline were used in all three incidents.
In New York, police and FBI were examining hundreds of hours of video from around the area and wanted to speak with a man in his 40s who was videotaped shedding his shirt near the Pathfinder.
The video shows the man slipping down Shubert Alley and taking off his shirt, revealing another underneath. In the same clip, looks back in the direction of the smoking vehicle and puts the first shirt in a bag.
They traveled to Pennsylvania for video shot by a tourist of a different person, and were evaluating the tape and determining whether to make it public.
On Monday, the White House for the first time clearly defined the attempted attack as an act of terrorism, without saying whether it was the work of a foreign or domestic plot.
"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," White House Press Secretary Robert Gibbs said when asked by Fox News how the White House would categorize the incident. "And I would say that whoever did that would be categorized as a terrorist. Yes."
Obama administration officials previously stopped short of declaring the incident terrorism.
New York Gov. David Paterson immediately called the attempted attack an "act of terrorism" after police were alerted to the bomb and cleared out Times Square Saturday night. But Attorney General Eric Holder on Monday said it was too early to officially designate the incident as terrorism.
Homeland Security Secretary Janet Napolitano, in several interviews since Sunday, has by turns described the incident as a potential or likely terrorist act, though she said investigators need to find out more about the origin of the plot.
"It certainly is something that I would not rule out," she told Fox News on Monday morning.
A Pakistani Taliban group released a videotape that appeared to claim responsibility for the incident, but New York City officials said they had no evidence to support that.
Fox News' Major Garrett, Catherine Herridge and Mike Levine and the Associated Press contributed to this report.