The suspect was already aboard Emirates Flight 202 when he was identified by the Department of Homeland Security's United States Customs and Border Protection.

Federal officials had placed him on a “no-fly” list hours before his arrest as a result of breaking developments in the investigation.

Counterterrorism officials send electronic notifications to airlines when watch lists are updated, but it is up to the airlines to check the web forum where the notifications are sent.

If Emirates airlines had done this, the airline would have been able to flag Shahzad when he purchased his ticket that night. Because they didn't, law enforcement officials were not aware of his travel plans until they received the flight manifest 30 minutes before takeoff, the official said.

By the time Customs and Border Protection officials spotted Shahzad's name on the passenger list and recognized him as the bombing suspect they were looking for, he was in his seat and the plane was preparing to leave the gate.

Officials called the plane back, the airline said. All of the passengers were taken off, and they, their luggage and the Boeing 777 were screened before the flight was allowed to depart, about seven hours late, at 6:29 a.m.

The Obama administration played down the fact that Shahzad had made it aboard the plane.