I watched plenty of movies that dealt with Psychological endings where the good guy usually is the one who did the crime. This game runs around that genre with all the emotion and violence. Now this game takes place 20 years before the comics. The other reason I feel Bigby is the killer is because he seems like he can't control his anger when it comes to certain situations. Maybe Bigby is suffering from Phychological disorder which makes him think someone else is the killer. Just think why else would everyone be coming after him? The Fables are scared of Bigby and feel he's a threat so the Crooked Man pays people to hunt him down. Maybe the blood in Bigby's apartment foreshadowed that he probably did kill someone and came into his apartment with bloody hands.
Bigby could have did it and runs away thinking Snow will hate him for it. That's why the screen for 105 looks like he's on a hill or something with bloody hands. Cry Wolf could mean he feels bad for what he did. Snow later finds him and forgives him. During that time Blue Beard becomes in control of the office.
I could be wrong, but this is just my thoughts. Do you think Bigby is the killer?