Wasn't it because of the bed sheet nearby? IIR, LE was viewing the area via drones, and the sheet caught their attention. I'm guessing that LE looked in the areas that they did because of the timeline... neighbor's camera recorded his truck backing into garage and leaving Monday morning, and LE knew CW arrived at work, so based on how much time passed between those events, they developed ideas about where to search.
Without the sheet and without NUA (yeah I'm in her fanclub for this), I wonder if they would have been missing much longer.
I could be wrong...does anyone else know if they only searched there after CW "admitted" certain info? I can't word it better than that because if his lips are moving, he's lying. All moo of course.
Edited because don't I always?? Typos on my silly phone with super funky auto correct and voice to text and whatnot.