My original guess was that the dairy guy was the killer and Peter just made unwarranted correlations between his method of killing and Newton and his own place in the scheme of things. Lack of sleep made him see Newton everywhere.

But then Newton really did show up.

So, now I'm confused. *g*

My first thought when seeing Walter in the store was "why isn't Astrid with him"?! *g* It was cool of the show to point out that she, an FBI agent, has basically become a babysitter and housekeeper; I was thinking the same thing.