Nice Red Herring At The Beginning
After we established, very early, that Cara's husband had been murdered and the David alternate had been murdered, I settled back and waited for the dead husband to be one of the split personalities. I was pretty sure he'd be popping out to say hello to his widow at any moment. So, good job going somewhere completely different!
I figure that must have been intentional misdirection because otherwise the husband could have died in a car wreck or any other way without going into all the detail of Christmas Eve/walking home from church/throat slit, etc.
Makes me think the original script might have been pretty tight and the reveal, with the hill people and the dirt and so forth, only got a little confusing and sloppy later on due to production constraints.