My theory is that Jason hit Ali in the back of the head because he didn’t see her face and he thought it was CeCe and then Mrs. D was burying Ali because she wanted to protect Jason and she thought Ali was already dead. She wasn’t right in the head at the time and she saw it as a way to both protect Jason from going to jail AND pin the blame on Spencer. Melissa probably saw Jason hit Ali but was protecting him because he’s her brother and she didn’t like Ali anyway so she didn’t really ever have a reason to want to tell police and out her brother.
Also, I have a feeling IF there’s a twin then either Mrs. D or Jason are the ones who might have one.
Either Jason is A or it’s “his twin” because there’s no one else who’s physically capable enough of making that jump. Besides maybe Jake, but that would make NO sense.
Also, there’s no way in hell they’d actually kill Ezra. This is just like the finale when everyone was asking “what’s in the trunk?!” and it was a pig. It’s just to keep people talking until June.
There’s also a slight possibility that if Mrs. D has a twin, that she’s the one who got killed at the very end. Or Mrs. D really did die and her twin plans on taking her place. There’s some room for a story there.
I usually don’t post theories on tumblr but I always read them so my apologies if this is all over the place. I just wanted to finally give my input.