What to do if you get something possibly stolen in school?

Today in school, I put my backpack near a doorway that is not very popular and left it there because my last period teacher doesn't let me carry my backpack to class. So since its the end of the day, I put my bag near the door and go to class. Then, I leave the classroom because I'm doing a project with my group for a video class, and I go to get my bag, and its not there?

I tried to talk to the school and they said to look in the lost and found, and I did, and it wasn't there. The person in the front of the main office tells me that I should check tomorrow for the lost and found again, and she proceeded to get the security guard to go with me and look at the live cameras. We then go to the spot, and then go ask a jgroup of 3-4 janitors if he seen a bag or took it and turned it in and they denied.

So then the bell is about to ring, and school is about to end and everyone is about to go home.

So what should I do tomorrow? My bag did not have any valuables in it, it was a black North Face backpack that only had my folders and notebooks, my glasses case, and the only thing someone would really steal if they looked at it; a pair of iPhone headphones.

Do you guys think maybe a custodian took it? Or someone stole it?

Depending if the cameras got the person who took it, you can't accuse anyone withouth reasonable doubt. Someone probably took it and threw it away. Hope this helps