Yeah, I did the same. I'm currently trying to take down the final boss first (before spoilering the spoilers) but it seems I've encountered a game-breaking bug, because the dude is wondering around [i]outside[/i] the room. His dot on the radar is beyond the walls, and when I use x-ray vision or what have you, he's just strolling around in... nothing. There is nothing physically where he is, just emptiness, and he's taking a stroll through it. Guess I'll have to reload an older save. :/