Shooting at paper targets is one thing.
Calmly (physical and mental calmness is necessary for good shooting) transcending the oldest of man's prohibitions is something else entirely.
There are a certain percentage of people who have no problem at all with this. They seem to be born that way. I've known numerous examples during my life and travels. Some of them make the news almost every day. This person (or these people?) is obviously one of them. A person like this doesn't need any extreme training with a rifle to accomplish his dirty deeds. Just marginal skills and minimal training.
My experience has been that one of the quicker ways to die is to assume anyone has any qualms about killing you or how or why he is going to kill you.
Not a problem if you have allowed evil to take over your thoughts and actions.