A government contractor brought highly explosive Soviet munitions on his trip home from Afghanistan that were not detected until he arrived at John F. Kennedy airport (search), federal officials said.

Shaun Marshall, a medic for defense contractor DynCorp (search), arrived at Kennedy Aug. 19 from the United Arab Emirates. He was trying to board a United Airlines flight home to California when he was pulled aside for a routine security check.

A search of his bags by federal screeners found what police bomb technicians described in an FBI complaint as a Soviet "projectile point detonating fuse" and a "surface-to-air and air-to-air cartridge."

Federal officials said they could not comment Tuesday on the risk that the munitions posed to the flight. But the city police bomb squad determined the munitions were "highly explosive," according to the FBI complaint.

Marshall also had five .50-caliber bullets and four small arms cartridges, which he did not declare to United as required by law, according to the complaint made public Tuesday.

The Transportation Security Administration (search) officers who searched Marshall's bags called police for the Port Authority of New York and New Jersey, which operates the airport.

"The fact that TSA located these explosives indicated the system is working," Assistant U.S. Attorney Lawrence Ferazani said.

Marshall, 26, told officers he was importing the munitions, which he believed to be inert, for use in DynCorp training exercises, and Port Authority police released him, federal officials said.

The FBI sent agents to arrest Marshall at his Riverside, Calif., home after the bomb squad analyzed the munitions and DynCorp officials said Marshall had no involvement in its training operations.

A Port Authority spokesman said he could not comment on why Marshall was released.

Marshall was released on bail in California and was expected to fly to New York City to be arraigned in federal court Friday.

He faces charges of placing explosives on an aircraft and trying to place ammunition on a domestic flight without notifying the carrier. He could face 20 years in prison if convicted.

Marshall's attorney declined to comment Tuesday.

DynCorp employees were warned not to bring dangerous materials back to the United States, company spokesman Mike Dickerson said.