The Algerian man caught at the U.S.-Canadian border earlier this month and charged with explosives smuggling was carrying a more powerful explosive than previously thought.

Ahmed Ressam was arrested Dec. 14 in Port Angeles, Wash. According to federal officials, he was carrying 200 pounds of a fertilizer called urea, four rudimentary timing devices and two jars of liquid.

The liquid was originally thought to be nitroglycerine, a relatively common explosive, but according to federal court documents released Tuesday, it turned out to be RDX, or cyclotrimethylene trinitramine, one of the most powerful explosives in the world. It is used by military forces around the world for demolition.

No blasting caps or other possible detonators were found, according to the documents.

Ressam, 32, is charged with five counts related to the bomb-making materials found in the car and could face up to 40 years in prison if convicted.

U.S. and Canadian authorities are searching for Abdelmajed Dahoumane, a man suspected of being Ressam's accomplice. The pair allegedly shared a motel room in Vancouver, British Columbia, for several weeks.

RDX can be combined with another chemical, PETN, to form the plastic explosive Semtex. It also could be combined with fertilizers, such as urea or ammonium nitrate, to create an even bigger explosion, said Van Romero, vice president of research at the New Mexico Institute of Mining and Technology.

"If you were going to bring down a building, you might use RDX," Romero said. "However, there are cheaper and more conventional ways of doing it."

RDX and Semtex have been blamed for a number of bombings around the world, including the 1988 destruction of Pan Am Flight 108 over Lockerbie, Scotland.