The U.S. system for checking suspicious travelers and airport security came under new scrutiny Sunday after an alleged terrorist bent on destroying a jetliner was thwarted only by a malfunctioning detonator and some quick-thinking passengers.

An apparent malfunction in a device designed to detonate the high explosive PETN may have been all that saved the 278 passengers and the crew aboard Northwest Flight 253 on Christmas Day. No undercover air marshal was on board and passengers subdued the suspect, Umar Farouk Abdulmutallab, 23, of Nigeria.

Abdulmutallab was hospitalized with burns from the attack and was read an indictment filed Saturday in federal court in Detroit charging him with attempting to destroy or wreck an aircraft and placing a destructive device in a plane. He was released from the hospital Sunday to the custody of federal marshals, who would not reveal where he was being held.

In November, Abdulmutallab had been placed in a database of more than 500,000 names of people suspected of terrorist ties. But officials say there was not enough information about his terror activity that would have placed him on a watch list that could have kept him from flying. Officials said he came to the attention of U.S. intelligence last month when his father, a prominent Nigerian banker, reported to the American Embassy in Nigeria about his son’s increasingly extremist views.

Still, in appearances on Sunday talk shows, Homeland Security Secretary Janet Napolitano said the traveling public “is very, very safe.”

“This was one individual literally of thousands that fly and thousands of flights every year,” Napolitano said. “And he was stopped before any damage could be done. I think the important thing to recognize here is that once this incident occurred, everything happened that should have.”

Even so, airport security and intelligence played no role in thwarting the plot. Abdulmutallab was carrying PETN, also known as pentaerythritol, the same material convicted shoe bomber Richard Reid used when he tried to destroy a trans-Atlantic flight in 2001 with explosives hidden in his shoes. Abdulmutallab is alleged to have carried the explosive in condom-like pouches attached to his body.

Despite being in the database of people with suspected terrorist ties, Abdulmutallab, who comes from a prominent and wealthy Nigerian family, had a multiple-entry U.S. visa. It was issued last year.

Napolitano said Abdulmutallab was properly screened before getting on the flight to Detroit from Amsterdam.

The administration is also investigating aviation detection systems to see how the alleged attacker managed to get on board the Northwest flight in Amsterdam with explosive materials, White House spokesman Robert Gibbs said.

No other flights were known to have been targeted. However, Gibbs says federal authorities took precautionary steps “to assume and plan for the very worst.” Napolitano said there is no indication yet Abdulmutallab is part of a larger terrorist plot, although his possible ties to al—Qaida are still under investigation.

The United States is reviewing what security measures were used in Amsterdam where he boarded the flight.

“Now the forensics are being analyzed with what could have been done,” Napolitano said.

Additional security measures are in place at airports around the world that are likely to slow travelers. Napolitano advised getting to airports earlier.

Congress is preparing to hold hearings on what happened and whether rules need to be changed.

“It’s amazing to me that an individual like this who was sending out so many signals could end up getting on a plane going to the U.S.,” said Sen. Mitch McConnell of Kentucky, the Republican leader in the Senate.

On Saturday, two Middle Eastern men thought to have been acting suspicious aboard a flight bound for Phoenix were detained and questioned by federal anti-terrorism authorities before being released. That incident -- and Sunday’s incident in Detroit -- led the Council on American-Islamic Relations to urge airline security personnel to avoid ethnic and religious profiling.

Gibbs appeared on ABC television’s “This Week,” NBC’s “Meet the Press” and CBS’ “Face the Nation.” Napolitano spoke on CNN’s “State of the Union” as well as on NBC and ABC. McConnell appeared on ABC.

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