Well, I'll start off by saying the animation on character design fit very well into the "creepy" feel. Back when I first found this, I didn't quite understand. I get it know.
He kills the lady at the end because when he says he doesn't have to wait anymore if he does things himself, he doesn't wait for her to die. He goes right ahead and kills her himself.
As for the change of clothes thing, maybe he does that because it's his way of showing his change. In the description it says a strange man begins to change his ways, so maybe this is how he expresses it. That or instead of waiting to get new clothes, he takes them right off the victims and wears them. I'm not exactly sure, but it sure adds to the mood.
Fantastic animation, plot and characters. I love it, it gives me the "spooky feel" for the day taht enjoy so much.