NEW YORK -- The Pakistani-American accused of a failed car bombing in Times Square is thought to have worked alone in the United States on the plot almost immediately after returning from a five-month visit to his native land, authorities said Wednesday.

They said they have yet to find a wider link to extremist groups.

Two new surveillance videos emerged of the accused bomber, Faisal Shahzad. Police said one video shows him in a white baseball cap walking away from the smoking, bomb-laden Nissan Pathfinder parked in the bustling heart of New York City.

The second video shows him buying a weak batch of fireworks in a store in Pennsylvania, according to the shop's owner.

Shahzad faces terrorism and weapons charges after authorities said he admitted rigging the Pathfinder with a crude bomb of firecrackers, propane and alarm clocks based on explosives training he received in Pakistan. Authorities said he was cooperating with investigators and did not appear in Manhattan federal court for a second day.

The government said Wednesday it would require airlines to check no-fly lists within two hours of being notified of updates, after Shahzad was able to board his Emirates flight despite being placed on the list. The airline apparently failed to check the latest version of the terror watch list that included Shahzad's name.

Until now, airlines had been required to check for list updates every 24 hours.

Authorities indicated that Shahzad, the 30-year-old son of a retired air force official in Pakistan, had launched the bomb plot alone almost immediately after returning to his Connecticut home in February from the visit to his native land.

A law enforcement official said authorities don't think there are any other U.S. suspects in the plot and that several arrests in Pakistan in the past two days were not related.

Law enforcement officials in Washington said they had not verified statements investigators said Shahzad had made that he was trained in Pakistan for the attack. All the officials spoke on condition of anonymity to discuss the case.

The FBI was able to identify Shahzad's name because of information Customs and Border Protection officials shared months earlier, according to a law enforcement official who spoke on condition of anonymity.

When Shahzad returned from Pakistan in February, he went through extra screening at U.S. Customs because of rules put in place after the attempted terrorist attack on Christmas Day. Customs officials noticed Shahzad had traveled to Pakistan previously, but for weeks, instead of months like his most recent trip. Shahzad came back to the United States without his family and without a return plane ticket.

When Customs officials come across people with suspicious travel patterns such as these, they send information along to the FBI.

As the FBI was following leads from the SUV left in Times Square, they found a phone number in the records of a throwaway cell phone that Shahzad had used when he was buying the SUV. The number matched a phone number Shahzad gave to Customs officials when he returned from his last trip. The FBI then contacted Customs about the match, and Customs provided other travel information on the suspect.