I don't think it matters or will be revealed who physicaly shot him, but it was on the orders of that Paris guy who owns the flash drive working with the black sheriff candidate. My guess would be the guy that ran Norma off the road in the previous episode, but I thought I saw him following Norma around the same time?

Anyway that scene where Norman transformed into Norma was creepy as hell. I was reading through this thread just now and someone asked if incest between Norman and his mother was ever brought up in the film. Well it wasn't in the original, but there was a crappy TV movie called Psycho The Beginning and the main explanation for Norman flipping was his mother had been sexually abusing him. Still this has nothing to do with the books, and Hitchcock had no involvement of course.