I have a question those readers in law enforcement might be able to answer. Who are the buyers of these catalytic converters? Fences, I would call them.
There are well developed and time tested methods of dealing with fences. Pawn shops come to mind. While nothing works 100%, nailing and prosecuting fences might make buying a catalytic converter too risky.
This isn’t a new problem. Back in the car biz day, I always checked under any trade vehicle I appraised. Customers often removed them (Hello, Wyoming) where emission tested wasn’t required.