Arne said, "What I don't understand is how killing him makes this a better world."

Violent murder. Senseless murder. Instigating murder and violence through founding a gang whose very existance was meant for terrorizing, extortion, murder.

Each case on it's own merits. Fair. Let's say, for the sake of arguement that he actually did do all the crimes he is accused of doing. Do you still want to keep him around?