New York, NY —

Law enforcement sources tell NPR they suspect several people were involved in the failed car bombing in Times Square over the weekend -- and that they were likely getting their orders from abroad.

Earlier, Mayor Michael Bloomberg had said the initial stages of the investigation had not turned up evidence of the involvement of a foreign-based terror group. But he said no lead or angle would be ruled out.

The NYPD says it won't comment on anonymously sourced material, and it's continuing to look at videotapes. Bloomberg says police are reviewing a number of videos taken in and around Times Square. He says additional footage of the SUV has been found.

"Police have also obtained other video images of the SUV traveling along 45th Street at Times Square," the mayor says.

Detectives have also spoken with a tourist from Pennsylvania who had been thought to have video of the scene. NYPD officials say that videotape did not yield anything of interest.

The White House on Monday characterized the attempted car bombing in Times Square as a terrorist act.

"That was intended to terrorize, absolutely, and I would say whoever did that would be characterized a terrorist, yes," White House Press secretary Robert Gibbs said today.

The NYPD has said the homemade bomb found in the back of a Nissan Pathfinder on West 45th Street Saturday night was large enough to kill several hundred people and shatter windows in a two to three block area.

Investigators have also spoken to the registered owner of the sport utility vehicle used in the failed car bomb attempt, but Bloomberg says the owner is not considered a suspect. The car left in Times Square was registered in Connecticut, where the owner on record was questioned Sunday night.

"We have no information whatsoever, no sense that they're involved, and if we have any information, we'll put it out," the mayor says. "We're doing the investigation, we're talking to everybody, we'll continue to do that."

Investigators also continue to seek a "person of interest," a white man in his 40s seen on surveillance video near the scene. On the video, the man is seen taking off a shirt and looking back in the direction of the car.

U.S. Attorney General Eric Holder told reporters that investigators have made "really substantial progress" and that "we have some good leads."

Meanwhile, Times Square is back to being the Crossroads of the World, filled with people -- and a few extra police officers.

"We're not going to be scared, we're not going to be cowed," the mayor said. "And as long as we have the best first responders and the cooperation we need from the federal government, we are going to be a safe city and we're going to go about our lives normally."

For related stories on the Times Square Terror Plot, click here.