The cop (spoilers)
I was going to use his testimony in the title but I realized that could be a spoiler too.
So why did they show the scene of the cop telling us there was a body that he found and about the tragedy? That really did spoil a major part of the ending. It doesn't make sense. Had they left that out then the tension at the end would have been ramped up to a fever pitch instead of us knowing in part what was going to happen. They took a lot of potential randomness out of the scene even though it still surprised