Who is the monster?

Once upon a time in a poorly drawn house, four people are casually standing around because I don't know how to animate.
But little do they know that once the lights turn off, once of them is going to die!
You need to find out who the monster is.

(I really didn't know what to make of the theme, I was thinking the player would do something like point at the murderer and say "You are the monster!", but hey, I still made a game.)

((The source is included in the Windows download under ./scripts, it runs on my own abomination of a framework - https://github.com/BearishMushroom/GLIC))

(((I also had no idea what to do in terms of music, so enjoy random chords.)))