What to do about someone stealing something of mine?

Okay so at my highschool the school provides every student with and IPad. There is a detachable back case on the back of the IPad. We were working in groups at the end of the day and my partners IPad ran out of charge so we used mine. I go to the bathroom then come back to see that it i now have a broken case. I have a certain scrape on my IPad case that no one has so I checked everyone's case and I didn't find it. I wasn't going to falsely accuse anyone so I kept the broken IPad Case. The next day my classmate was looking suspicious and I checked his case and it ended up being it and I'm 100 percent sure about it. I considered my options and realize I have three choices. 1. To steal back the case. 2. To tell a teacher of principal and see what they could do. Or 3. Let him get away with it and keep the broken case. (Most likely my last option) I know it sounds silly but the case is $20 and I don't take stuff like this lightly. This kid is bad and constantly lies. What would you recommend me doing. Stealing it back is risky. Telling a teacher could cause too much drama and hate towards me. Thank you for your answers!

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