Hmm...y’know I know this seems to early for theories but honestly I kinda want to do this now since it been bugging me. This might contain some spoilers.
So probably picking a certain person might change the murderer, since I remember one of Grizz’s messages did say it’s possible to be in a relationship with each and everyone of them, but if it doesn’t change the murderer then honestly I would put Sal or Dean up there to be the murderer. I can’t assume they got possess or something to cause suicide since some of these deaths doesn’t make sense to be suicide (especially Tyson’s) and well Sal’s and Dean’s ending wasn’t really murder but more suicide seeing the evidence there to how it seems to happen. Mostly think Dean the murderer in my opinion that is, people can disagree which I’m fine with since it’s a theory and kinda wanna put it out there. (Sorry if I comment too much it just this visual novel is so unique and cool!)