Marvellous.

You are. I'm an inmate, the same as you. And considering the difficulty, if not outright impossibility, of proving a negative, I suggest you take proof from simple reason. If I were a kidnapper, murderer, or monster, it would be counter-intuitive to warn you about myself. You have nothing I want, I currently stand to gain nothing by causing you harm, and you can see for yourself that I am too rational to be a deranged psychopath. Therefore, my proof is, once again, my complete lack of motive.