If you find someone's laptop or Iphone and keep it, is it stealing?

I just came here so I can get an answer faster. Ok here goes, I needed a new laptop and recently got one. I just got it maybe 3 weeks to a month ago. I saved the serial number and model number paper and everything, thankful. Anyway I was at my university one day and had a lot on my mind, and I accidentally left my laptop in my class. I didn't realize it until I got in my car and was heading to the store.So, I turned around and wentback to the class room, not there. Then I went to lost and found and this lady was nearby and overheard me talking to the lady at lost and found. This nice caring lady thankfully asked me about it and what classroom it was in, then told me she saw her teacher pick it up. She told me the teacher's name. Then I had the lost and found lady call her. I tried to call her and no one picked up. The next day, I filed a police report and then I got a call back from the police officer saying I can pick it up at lost and found on campus. I picked up my computer and everything that was originally on it was gone. The computer was wiped clean. Is there a way I can press charges against this teacher for hacking my computer, and even though she found it, is it still stealing since she took it home and tried to keep it? Also if she reset my computer, does that mean she had access to my personal information? I did have a password on my computer, but I guess that doesn't really protect anything. I also did have a guest account, so that friends or family can use my computer when they come over if needed. How can I get proof that she hacked my computer and reset it, and what are the penalties for her?

Sue her.