The airline passenger accused of trying to ignite explosives in his sneakers had a homemade bomb that could have blown a hole in the jet's fuselage, an FBI agent testified Friday.

Richard C. Reid, a 28-year-old British citizen of English and Jamaican descent, appeared at the bail hearing in federal court in an orange jail jumpsuit, his hands shackled.

U.S. Magistrate Judge Judith Dein ordered him held without bail, saying Reid's "violent and assaultive behavior toward the flight attendants" showed he would pose a danger to the public if released.

"The evidence is that the defendant was trying to set off an explosive device on a flight with approximately 183 passengers and 14 crew members on board," Dein wrote. "He acted with callous disregard for the safety of others, and, in fact, appears to have intended to cause them all serious harm, if not death."

She also noted he has at least 16 prior convictions, mostly for theft, and has lived mostly in Europe at various locations for short periods. He told investigators he was never "officially" employed, but worked at construction and as a restaurant kitchen helper, Dein said.

Reid was arrested Saturday after American Airlines attendants allegedly saw him try to touch a lighted match to his sneakers during a Paris-to-Miami flight. Reid was overpowered by flight attendants and passengers, and the Boeing 767 was diverted to Boston.

FBI agent Margaret G. Cronin, a specialist in crime aboard aircraft, testified that Reid was carrying "functioning improvised explosives, or, in layman's terms, a homemade bomb."

She said an explosives expert concluded that if the sneakers had been placed against an outside wall and blown up, they "would have blown a hole in the fuselage." Reid was in a window seat.

Cronin said preliminary tests last weekend on Reid's sneakers showed the presence of triacetone triperoxide, TATP, a highly volatile plastic explosive. She said she did not know if the explosive devices in Reid's sneakers could have been detonated with a match, as Reid allegedly tried to do. The sneakers are undergoing further tests.

A global investigation is under way to determine whether Reid had any ties to terrorist groups. The issue did not come up at the bail hearing.

Reid was charged with intimidation or assault of a flight crew, which carries up to 20 years in prison. The FBI has indicated that additional charges are likely.

Arguing against any bail, federal prosecutor Colin Owyang said Reid had "essentially no verifiable address anywhere in the world" and might flee.

Owyang said Reid had been living in hotels in Paris and has no known friends or relatives in the United States, and no work visa or immigration papers.

Reid's court-appointed lawyer, Tamar Birckhead, did not specifically argue that Reid be released on bail but asked the judge to rule soon so the defense could begin work on its case.

U.S. Attorney Michael J. Sullivan, speaking to reporters afterward, said that besides a valid British passport, Reid also had a single page from a separate British passport. It appeared he had no accomplices on the plane, Sullivan said.

U.S. officials are trying to corroborate claims from low-level al-Qaida prisoners that Reid trained with them at Osama bin Laden's terrorist camps in Afghanistan.

The officials warned that the prisoners could be wrong, or lying to confuse or gain favor with their interrogators.

Officials have also confirmed that Reid attended the same London mosque as Zacarias Moussaoui, who is charged with conspiracy in the Sept. 11 terrorist attacks.

Birckhead, the defense attorney, has said she's unaware of any evidence tying Reid to terrorists.