Warning! Spoilers Ahead!
If you still haven't played this brilliant game, I suggest you do so. Even if you're not a zombie games fan, it think you'll find it quite enjoyable.
Now, as many of you know, the game actually has two different endings. One is the "canon" heroic ending, the other shows Randall as a cold-blooded killer who went mental after the apocalypse started and killed all of the survivors from his group during the course of the game. But I have a third theory.
The diary shows that Randall was a bit psychotic, seems that he even killed two girls in the forest he worked in... Now the setting of this game could be a lot more than a simple zombie apocalypse. The things are called Shadows... Maybe shadows of his past, his psychological problems? The whole story and setting might actually be showing Randall's personal hell in his brain, the apocalypse might not even be real, it might be just a depiction of what's going on in Randall's head.
Think about it. How did the Rat know everything about him? Maybe because - He's not real! My guess is that the Rat is the embodiment of the secluded part of Randall's personality. The Shadows could represent his mental problems, the survivors people he hated or his victims or something, and the Randall you play in the game could be the tiny bit of his mind that's still sane and normal, and he's trying to fight and get through the apocalypse in his mind, that is - insanity.
The ID cards you collect during the game all bear the names of real-life serial killers. The mementos you collect off the random corpses and your friends' bodies after their deaths... Serial killers tend to collect mementos of their victims. Randall kills the two girls, very soon the "apocalypse"/insanity starts, and he then proceeds to kill his family. It all coincides, doesn't it?
Long story short:
What if - Randall was a serial killer, the two girls, his wife, daughter and the "survivors" - his victims, the New Law were the law enforcement/police, and the start of the apocalypse - just the boiling point of Randall's psychotic mind?
Post your opinions on the theory if you have an argument to support or even oppose this theory.