OAKLEY (KRON) — Police are warning residents in Oakley of a recent string in thefts of catalytic converters from Toyota cars.

Police say the robberies have been reported across the city and tend to happen between the hours of 2 a.m. and 5 a.m.

Up to 15 cars have been targeted in the past three weeks, and police think Toyota’s may be the target because they’re higher off the ground than other makes.

Without the catalytic converters, the cars can operate, but sound as if there is no muffler, rendering the cars unfit for travel on California roads.

Police believe this is a two person scheme, and that targets have been previously scouted.

Anyone with information is asked to call Oakley police.