Someone stole my hat what can i do? I know who did it.?

Like, I let this one girl borrow my hat but then she says that (i'll just give them fake names) Kevin or Bronco has it because Bronco took it from her. Now I've known Bronco since the fourth grade so if he has it i'll get it back, but she tried to get it back from Kevin today but she said he was being an ******. Now i want to tell Kevin to have my hat or I drop him but at the same time I don't want to misuse my martial arts. But i don't want to tell or I'll be known as a snitch. What do I do?