This reminds me of the case of Kiplyn Davis. Everyone knew that the boys were guilty and they had bragged to many teens; but it took a federal grand jury to get them on anything. The police really botched Kiplyn's case in the beginning; or her case may have been solved sooner.
Perhaps someone should push for a federal GJ in this case.
Part of the problem is they haven't found a body or any hard physical evidence. I know people have been convicted before with no body found. However, do the Belton PD really not know, not care or is it a possible coverup?