The phrase "murderous psychopath" refers to a person who has a mental disorder characterized by violent and impulsive behavior, and a tendency to kill others. Full definition
Instead this «new» Joker, as portrayed by the sadly deceased Heath Ledger, is an absolutely maniacal murderous psychopath as co-star Michael Caine said in an interview. (scifimoviepage.com)
A bunch of murderous psychopaths converging on a single location... what could go wrong?! (nerdlocker.com)
This is opposed to the typical horror genre where things are just creepy, or slasher style horror where there is a single murderous psychopath with an axe / chainsaw / knife / whatever. (16bitdad.com)