They say that exhibitionists are pretty harmless, but the truth is, no one really knows.
You assume that he was waiting for a female prey to kill, I think that he merely wanted to exhibit himself, but could have noticed the girls taking a video, and that made him angry, so he removed the witnesses.
His gait is odd, but I don’t think there is a problem with his legs. (Could be, of course, neuropathy or other things could have caused it. Why do I think he is not healthy?).
But exhibitionist-like behavior could create this peculiarity, too. I am not insisting, just an idea.