Hmm let me see, it has been a while since I was there so I dont remember completely. Did you miss any levers, I remember that there should be atleast one though I do not know if it was the one you need for the imp. have you tried alt and scrool around the prison, it is not so big? Anyway try doing a search and clear the area. There is no special trick or riddles for the prison so it is just a matter of finding the key. Hope luck will shine upon you
