Yeah, I just mentioned there were a few pages near the beginning where the reputation didn't go up like it should, but I ended with a rep of 14, so I guess I was doing well.
I named the guy who always seems to be the likely suspect, but within the story terms I mainly based it on the clue you find concerning one of the victims and then later when you go talk to him. (During that scene, I thought "Well that's the guy right there and he's almost bragging about what he's done.")
Plus, I've always personally believed Jack had to be a doctor of some sort. (Or at least have medical knowledge)