What if someone steals something?

This situation is actually very helpless. Even if you know people around you, there is no conclusive evidence and no good way to identify them.

So this happened first. You should learn to protect your things better, pay more attention, and don't be particularly casual. If you pay special attention, he has no chance and can't help it.

Secondly, this incident must be kept secret, so that people around you know that you have lost something and remind everyone to pay attention. If you tell a story, everyone will pay attention to it at ordinary times, so the chance of being stolen will be reduced.

What I said above is that there is no way. After all, there is no evidence. If there is any surveillance video that can prove who stole it, it is the most direct way to find him directly and make it clear.