You get 1200 from killing someone.
Blue mobs = -1 point
Green mobs = -3 points
White mobs = -5 point
Orange mobs = -8 points (or maybe 7?)
Red mobs = -10 points
My archer became a murderer and it only took like 30 mins to grind off. And because I was surrounded by botters, I never died
Also, there is no penalty for a murderer killing another murderer.
I tried this out before, I was murderer, saw a murderer, killed a murderer, and got no additonal murder points.