>>>>If it was all planned out ahead of time he would have known exactly what to say.<<<<
What about the fact Scott had researched the directions of tides and currents in the bay? That indicates preplanning and premeditation.
OMG!! There are tons of things he did that show PREmeditation!!. Making anchors, buying the boat secretly, PROPHESYING her disappearance and the fact that THIS would be his FIRST Xmas without her. Secret storage unit, of course all the computer research. And on and on it goes.
That could have indicated pre-planning but by not having a consistent alibi he left himself wide open as the prime suspect. If he planned it ahead of time you'd think that would be the first thing he concerned himself with, but then again everything about this guy appears inconsistent.