I think these people are mentaly Ill. What makes somebody kill someone else, espicialy this way. It has been a long discussion if movies make people act like this. Personally i think there has to be something wrong with people beforehand.
Movies do not make people kill, people make people kill. I hope these three people are going to be locked up for a very long time. I saw a lot of horror movies but it never made me kill someone who i did not like.