My phone got stolen and I think I know who took it, please help?

I left my phone in my pants pocket in the gym change room at school and I came back after class and it was gone, and I know it got stolen because my stuff was moved and I remember putting it in my pocket in the morning. I think I know who it is because this persons phone broke that they got for christmas, and I've seen him take money out of someone elses bag for the vending machine and he told me I'd better not tell anyone. Plus he seems like the person who would do something like this. I've canclled my phone. this person is bigger then me too and I haven't told anyone about the money thing yet but am starting to consider to. I'm kinda afraid of being beat up but also just want my phone back. I would appreciate any help you can offer! Also do you know of anyways that I could possibly get my phone back? and can the serial number be SAP# or is it Serial# or ID# and where would I find this on the box that I got my phone in? My phone is a samsung gravity touch.