Game over guys I figured it out. I know who de murderer is and why.
It's the skunk from the coffee shop when Dave remembers how he met Dean. Because it's the only incidental character with a sprite.
He overheard Dave or one of his friends about the trip to the mansion. He always wanted to go to a mansion, and took deep offense when he wasn't invited. Maybe even had feelings for Dave. So he planned his revenge and set a plan in motion to murder everyone. It's painfully obvious.
Lol jk. I jus wanted to ask for a hint for the first password :c the easter egg.
