They are practically sitting on the ramp at this location. Woudn't trailers pull up and slide their boats out there. Wouldn't the bottom become very impacted at that spot. I imagine many things would drop off trailers or boats on that slip. Anything left there would become compacted....at least that is my thinking and if they are searching between the two docks.
So did the perp walk out there on that dock and slip her in the water. Not w/o being contained, imo. Off to the side, without using the ramp area, she could have been placed w/o contained. She could have even been buried there...but if this happened that night on the 9th, there would be no time for that....and if the van was used their would be evidence of mud, etc. (if they buried). If the walked, no mud but they would need concealment.