If you couldn't tell from the title, this is a 'theory' and not a pasta.
There will be spoilers, but I will warn you when the spoilers are coming.
The Theory Edit
Just like the title says, I have a little 'theory'. It's not much of a theory, but it's just something else I thought of in the game. So, I think the killer, which,
The actual 'killer' is Josh
End Spoiler Alert
So I think the killer is you, as explained in the therapy sections of the game. The killer is, literally, YOU. The player, and the therapist represents other people's reactions to the choices you make. I noticed this when I heard a few youtubers saying that people always talk about "Oh, you made a stupid idea" and all,
SPOILER ALERT[kind of?]
and in later dialogues when the killer is revealed to be the person in therapy(Notice how they are in the same room - Dr. Hill (therapist) is shouting at the killer for torturing his so called 'friends'. The killer in the therapy room, does nothing. This is representative that, you can't do much about what other people say. This more or less goes towards gaming commentators that play the game, where they can't directly communicate with the people questioning the players decisions.
End of Spoiler.
Another 'theory' that follows the same guideline as that Dr. Hill(Therapist) may represent the media, and how they question everything you do.
So I came up with this 'theory' at random - it just came to me. What do you guys think about it? I doubt that they did that intentionally, but it still sounds cool and an interesting topic to think about when you think about, at least for me.