FBI joins probe of explosives found under O.C. bridge

   The FBI has been brought in to help investigate a cache of explosives -- grenades, blasting caps and fuse igniters -- that was found in a backpack under a bridge in Placentia on Monday.

Orange County bomb squad officials were brought in after the backpack was discovered about 8:50 a.m. Monday by people working in a drainage ditch, said Orange County Sheriff's spokesman Jim Amormino.

After cordoning off the area, bomb technicians detonated the contents of the backpack, including six grenades,  blasting caps, fuse igniters and blasting powder. For several hours, Lakeview Avenue between Orangethorpe Avenue and Eisenhower Circle was closed to traffic.

Authorities said they are looking for a suspect and have asked the FBI for assistance.

"It was a dangerous situation," Amormino said. "It could have caused major structural damage to the bridge."

He said that the suspect appears to have a good understanding of explosives.

"Possibly in the military," he said. "Possibly somewhere else. We don't know yet."

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--Nicole Santa Cruz