WASHINGTON — Investigators still piecing together a brazen attempt to bring down a trans-Atlantic airliner said yesterday that the suspect tucked a small bag holding his deadly concoction on his body, using an explosive that easily would have been detected with the right airport equipment.

The man's success in smuggling and partially igniting the material on Friday's flight to Detroit prompted the Obama administration to promise a sweeping review of aviation security.

Adding to the airborne jitters, a second Nigerian man was detained yesterday from the same Northwest flight to Detroit after he locked himself in the plane's bathroom. Officials reported that he was belligerent but genuinely sick, and that, in an abundance of caution, the plane was taken to a remote location for screening before passengers were let off.

Investigators concluded that he posed no threat. Despite the government's decision after the attempted Friday attack to mobilize more air marshals, none was on the Sunday flight from Amsterdam, according to a government report obtained by The Associated Press.

Stiffer boarding measures met passengers at gates as authorities warned travelers to expect extra delays returning home from holidays. White House spokesman Robert Gibbs announced a review of air safety on two broad fronts, saying that the government will investigate its systems for placing suspicious travelers on watch lists and for detecting explosives before passengers board flights.

Both lines of defense were breached in an improbable series of events Christmas Day that spanned three continents and culminated in a struggle and fire aboard a Northwest jet shortly before its safe landing in Detroit. Law enforcement officials believe that the suspect tried to ignite a two-part concoction of PETN and possibly a glycol-based liquid explosive, setting off popping, smoke and some fire but no deadly detonation.

Nigerian Umar Farouk Abdulmutallab, 23, an Islamic devotee, was released from a Michigan hospital in the custody of federal marshals yesterday after being treated for burns. He is charged with attempting to destroy an aircraft and placing a destructive device in a plane.

Abdulmutallab's lawyer said that he is now in a federal prison in Milan, Mich.

Homeland Security Secretary Janet Napolitano hastened to assure people that flying is "very, very safe."

She said that the suspect in Friday's attack "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."

That brought a sharp rebuke from Rep. Peter King, R-N.Y., the top Republican on the Homeland Security Committee. "It's not reassuring when the secretary of Homeland Security says the system worked," King said. "It failed in every respect."

Sen. Mitch McConnell, of Kentucky, the Republican leader in the Senate, said, "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."

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. No undercover air marshal was on board and passengers and crew subdued the suspect when he tried to set off the explosion. He succeeded only in starting a fire on himself.

Law enforcement officials said that Abdulmutallab hid a condom or condom-like pouch below his torso containing PETN, the primary ingredient in detonating cords.

Airport "puffer" machines that blow air on a passenger to collect and analyze residues would probably have detected the powder, as would bomb-sniffing dogs or a hands-on search using a swab, the officials said, but most passengers in airports only go through magnetometers, which detect metal rather than explosives.

Abdulmutallab told authorities after his arrest that his plan originated with al Qaeda's network inside Yemen, a link that the U.S. government has avoided making so far. Napolitano said that there was no indication yet that Abdulmutallab is part of a larger terrorist plot, although his possible ties to al Qaeda are still under investigation.

Abdulmutallab had been placed on a watch list with more than 500,000 names in November, but not one that denied him passage by air into the U.S. Officials said that 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.

Despite that red flag, Abdulmutallab was not elevated to more exclusive — and perhaps manageable — lists of some 18,000 people who are designated for additional security searches or barred from flying altogether. Napolitano said that that would have required "specific, credible, derogatory information" that authorities didn't have.

A U.S. official said that the father's concerns were shared among those in the embassy, including liaison personnel from other agencies based there, such as the FBI. The alert was then relayed to Washington and again shared among agencies such as the State, Justice and Homeland Security departments, said the official, who spoke on condition of anonymity.

Nigerian Information Minister Dora Akunyili said that Abdulmutallab, who was living in London, sneaked back into Nigeria to catch the flight that would take him to Amsterdam and Detroit. She did not elaborate on how he entered the country.

Abdulmutallab had a U.S. visa issued in June 2008 and valid through June 2010.

Just as passenger shoe searches became the order of the day after Richard Reid tried to blow up a trans-Atlantic flight in 2001 with PETN hidden in his shoes, the latest attempted assault could bring new layers of screening and delays. Among the possibilities: fuller and more frequent body pat-downs and scanning.

Gibbs appeared on ABC'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. King appeared on CBS; McConnell appeared on ABC. *