ISTM that there are three possible reasons to dump the bodies where they were found.

The first is that the bay is a common place for bodies to be dumped. It has happened before and since. However if this was the case, why not dump both bodies in the water?

The second is to point at Scott. It was highly effective, however in that case why not leave both bodies on the shore?

The third, and most compelling reason, was to ensure that Conner was properly buried. If, as I have concluded, this was a fetal abduction, then the woman who did this thought of Conner as “her baby” and cared about his disposition. She wanted him properly buried. In her twisted mind she despised Laci and wanted to toss her away. This is the best explanation for the choice of two locations to deal with the two bodies.

Perhaps we can get a psychological analysis of this!