EL CAJON, Calif. -- A man was behind bars Monday after a hand grenade was found in the trunk of his car in El Cajon, police said.

Geoffrey Curtis Killen, 29, was arrested in eastern El Cajon around 9 p.m. Sunday after the device was discovered, said Lt. Tim Henton, adding that businesses near the intersection of Main Street and Greenfield Drive were evacuated.

An officer pulled Killen over because his vehicle's registration was expired, Henton said.

The lieutenant said the trunk was searched after the officer decided to impound the car on grounds that the registration had expired more than six months earlier, he said.

The sheriff's bomb squad and agents from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives were called in to render the device safe, he said.

Killen was booked on suspicion of possessing an explosive device and was being held in lieu of $100,000 bail, according to jail records.