Is it normal to dream of killing people?

In the dream, I had to kill this guy. I came here specifically to kill him. I found him in a room with his daughter. He was painting her as a mermaid. I closed the door and locked them in. Guards ran at me, trying to stop me so I killed them. My target inside began trying to break down the door. I unlocked it and stepped back. He came out and we started fighting. Somehow I ended up at the doorway of the room trying to reach the girl but the man was holding me back. I grasped for her, but ended up snatching the unfinished painting. I ran back out. Since I didn't see his daughter I thought I had killed her accidentally. He thought I killed her as well. He went after me like a mad man. I killed him, completing my mission. I found the girl later. She was in shock, so I left her alone. I noticed that she had short hair. I remember specifically studying the painting. It was the girl but as a mermaid. At the end of the dream, I smiled. I dreamt that I enjoyed killing them. Please note that I am normally a very happy, optimistic, colorful person. I've never had any dreams like this before.