What can I do if an ex-employer stoled from me?

So I work at an automobile shop. The owner there sold his shop to a company that took over. The new owners took over, but the previous owner has keys still to the place, and he went in one night and stole personal belongings (like tools) from all employee's work stations. The new owners said they would change the keys to the shop, but they have not and the previous owner came in again and stole from all of us. The previous owner had always been very unpleasant. For example, he always took a long time to pay us for our work. There's some other devious things that he would do. I really don't know why he's coming in and stealing, if he has resentment or is on drugs (that's another issue). Do I file a complaint with the police or is this an employment issue?