[Irene Adler]

"Why would Scott talk about going to the water at all, had he taken Laci's body out there in a tarp and dumped it? There were no witnesses. Why would he place himself at the general scene of the crime?"

I am guessing because he was worried someone might have seen him at or around the scene and might remember having seen him, and he was covering that potential situation. Also he didn't expect Laci's body to break loose from the concrete he had it tied to. That's what I would guess. All accomplished liars mix fact in with their fiction to make the fiction more convincing.