Make them more curled up.And adding some blood to the model would help make it seem more killer.

What I would like to see is something along the lines of Kliener covered in blood, holding a bloody knife, with his own animation that either stabs people in the back or slashes their necks. Also, Health would have to be raised so it would be a real enemy. These are just suggestions, so you can do what you feel like doing. Also, ™.