SocksAndShoes
Banned
People saying "this isn't your problem OP" are a bit off, OP has to live with this in a place with a potential thief and he's been accused of theft. It's very much his problem at this point.
OP: I would get them both in a room and talk about it. If he's lying it might be obvious and the blame could shift from you to him from her perspective. That'll take some of the pressure off.
You'll still have to deal with living with a thief though if it turns out to be him, but it's definitely better to take a situation like this head-on than putting your head in the sand.
OP doesn't need to play Dr. Phil. The roommate who had money stolen needs to involve the authorities. OP has made himself more culpable here by looking through someone's wallet. Poorly handled all around.