Instructions
Play the game to encounter psychopaths. Psychopaths show up in the form of minibosses throughout the game. You will be able to distinguish a psychopath from the regular zombies because the psychopath will have a unique skill set. For example, one psychopath drives around on a motorcycle.
Kill the psychopath. Use your imagination to figure out ways to hurt the psychopath. Generally, you can hurt a psychopath only during certain strategic moments. For example, a psychopath may jump from one object to another and let his guard down. Attack during a psychopath's moment of weakness.
Consult a strategy guide, such as IGN, if you die too many times trying to kill a particular psychopath. Read the guide's information to learn the weaknesses of specific psychopaths. Follow the tips of the guide to kill the psychopath. For example, case 2-2's psychopath Carlito swings a powerful sniper rifle at you. You need a Katana to defeat him. The second-floor on the west side of the mall has an edged weapon shop. Pick the Katana up from there. Strike Carlito with the Katana and immediately back away. He will then swing his sniper rifle at you and miss. Repeat this multiple times to kill him.