This is a very interesting scenario. If the coroner can somehow prove that the man was still alive when the other man shot him, then I may agree. (I say 'may' because there are other extenuating circumstances that may come into play.) However, if his movements were involuntary reflexes caused by the nerves still being active, then the man probably should not be accused of murder, but maybe abuse of a corpse. This is one of those things that lawyers and prosecutors have to toss around between them.
When a person dies, so does the brain, generally speaking. However, the nerves may still send signals to the spinal cord, which in turn will cause the nerves to twitch. I don't have much knowledge regarding medicine, but I have seen people that have died and still have nerves twitching and fluttering. It's sort of like when a person chops off the head of a chicken and the chicken still wants to run around, thus the saying, "Running around like a chicken with its head cut off."
