HELP!!! I can't find Mr. Crowley in Fallout 3!!!?

I completed the quest "You gotta' shoot em' in the head" and I didn't realize that I needed the keys to get the power armor. I went back to underworld and he wasn't there!!! I checked Fort Constantine, and I still can't find him! It has been like, a week "in game" and he is still no where to be found. HELP?!?!?