A van driven by a man wearing four bulletproof vests rammed head-on into a patrol car Friday, not long after someone in the van shot another sheriff's deputy in the back, authorities said.

The van and patrol car burst into flames after the collision. About 75 people in a square-mile area were evacuated after the suspect, wearing four body armor vests and camouflage clothing, told officers pulling him from the burning wreckage that a pipe bomb and ammunition were in the van.It was unclear what the motive for the attack was.

"This may have been an ambush of one of our officers," said Undersheriff Lou Blanas. "We don't know the motive. We don't know why this occurred."

The bomb squad searched the charred remains of the van, found fragments of a possible bomb and decided it had detonated during the fire, deputies said.

Deputy Mike Butler's bulletproof vest protected him from two shots to the back and he suffered only a graze to the shoulder.

The patrol car driver, Deputy Jared Beck, was hospitalized in good condition with sore ribs.