Borrow a Have-a-heart trap. Try the Humane Society, and animal/cat rescue group, or your local Animal Control people. set it up in the attic or wherever with some apple and peanut butter. You'll get him quick enough that way and you won't have to hurt him. Be sure to check it twice a day!
Read about them here:
http://www.for-the-love-of-cats.com/HAVAHEART.html