His demeanor is so off. One could say he was in shock that night and so that is why he appeared calm during the police interviews. However, it seems like it is just him and his personality. He was called meek by a witness. In every interview, he appears very calm, under control, and quiet in nature. All of that is perfectly fine. I know many people like that.
The difference is, when a person gets beaten up for the first time in their life, I would think even the quietest person would exhibit a little more adrenaline in their voice. On top of that, I would think that any person who pulls a gun for the very first time on a human being and shoots at them would be very shaken up. To find out that you actually killed a human being (even if he was the worst person in the world) would still be very unsettling for most people. His behavior bothers me.