you have a standard answer

Since I watched a lot of crime fighting dramas on TV, here are some points for you to consider:

1. How expensive the item is, If it is a less expensive item, offer to buy one for him to replace the old one and return it. If it is an expensive one, asking him to return it may not be a right answer. The person might not be suitable to continue to serve as a law enforcement agent. You might need to consult with the supervisor immediately.

2. How often he takes the possessions of other people items? if it happens very often, you might need to discuss with the supervisor.