A Federal investigator testified Friday that the man accused of trying to detonate explosives in his shoes on a transatlantic flight, Richard Reid, was carrying a working, improvised bomb.

He spoke at a brief hearing on whether suspect Richard Reid should continue to be held without bail was held in Federal Court in Boston. The U.S. magistrate agreed with prosecutors that Mr. Reid, who was arrested Saturday, should remain in jail until his trial.

A special agent of the U.S. Federal Bureau of Investigation testified at the hearing that Mr. Reid was carrying functioning improvised explosives in his shoes. She said that if placed against an outside wall of the airplane and blown up, they would have blown a hole in the fuselage.

Mr. Reid, 28, a British citizen, is charged with intimidation and interfering with a flight crew. The offenses carry 20 year sentences. Authorities have indicated other charges could be filed later.

He is accused of trying to set off the explosives in his shoes with a match. He was subdued by passengers and members of the flight crew, aboard an American Airlines jetliner that was originally headed from Paris to Miami. The plane was diverted to Boston because of the in-flight incident.

Investigators are retracing Mr. Reid's travels in Europe and the Middle East to determine, if he has ties to terrorists. His court-appointed defense attorney says she knows of no evidence linking her client to terrorists.