The Pakistani-American accused of a failed car bombing in Times Square is believed to have worked alone on the plot, authorities have said.
They said they have yet to find a wider link from suspect Faisal Shahzad to extremist groups.
Two new surveillance videos emerged of Shahzad, one of him in a white baseball cap and a dark jacket 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 is seen buying six to eight boxes of a consumer-grade product in Pennsylvania, which a spokesman for the shop said "wouldn't damage a watermelon".
Shahzad, 30, 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.
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.
Shahzad was hauled off a Dubai-bound plane he had boarded Monday night at Kennedy Airport despite being under surveillance and placed on the federal no-fly list.
"I was expecting you. Are you NYPD or FBI?" Shahzad told Customs officials who came aboard the jet to arrest him, an official with knowledge of the investigation said.
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.