Thief?

Today was very surprising. When we were having some practices at anatomy lab suddenly our friend lost her cellular phone. Because it's a closed practice so the suspect is among us. But who? Everyone at that room was clear when we do some investigations. Eventough thera are many of us that had gone home at that time it doesn't mean that they are the suspect. We still don't have any clue. But the only thing bothered me is i feel something's strange at that time but i can't remember what was that.