It wasn't Cheryl Blossom. Hal Cooper was innocent. Not even Hermione Lodge nor poor Smithers pulled the trigger that killed the heir to Blossom Maple Farms!
SPOILERS... (And yes, I'll wait until the show wraps up in the west coast...)
I totally didn't think that "Riverdale" would go with the obvious creepy, crazy murderer -- but I totally was off-base. Jason Blossom was murdered by his father, Cliff Blossom.
We still don't know the details and won't figure them out until next week, but Cliff and his son had a huge fight on the day that Jason fled Riverdale. Jason rejected some secret about the family business and Cliff couldn't let that secret become public. So he had the Southside Serpents kidnap Jason before he could flee Riverdale and stashed him away in the basement of the Whyte Wyrm.
Jason got beat up for a while by one of the Serpents until Cliff entered the room and shot his in the head. The body was frozen for a while and then FP Jones and Joaquin (Jughead's father and Kevin's boyfriend) clean up the mess and tossed the body in the lake after the police stopped dragging it.
After all, where better to hide a body than the first place that the police previously looked?
By the end of Episode 12, everyone knows that Cliff Blossom shot his son. It was on video. Cliff was confronted by Cheryl and he ended up hanging himself in the maple syrup barn.
We still don't know the dark secret behind Blossom Maple Farms or why Cliff actually killed his son. We saw packets of something -- presumably drugs -- hidden away in the maple syrup barn, so maybe it had to do with drugs. I'm still not convinced!
Tune in next Thursday night at 8:00 PM CST for the final episode of "Riverdale" Season One! Hopefully, all secrets will be revealed!