Another thing that strikes me in these cases is how quickly the perpetrators want to get on with their plans, causing them to say and do odd things. While everyone else is in the midst of shock and concern, they've already "moved on", they know what has happened since they planned it, and they did it, and they are ready to move onto the next stage of their plan.
When NU called CW about the welfare check, he starts rambling to her about separation. NU is bewildered, at this stage she's just concerned SW has had a medical episode and she wants to check on her. She even said something along the lines of "why are you talking about this now?". She realizes CW isn't going to help, her anxiety rises, and thankfully she had it in her to not rationalize her gut feeling away and calls the police. She knows "something" is wrong here.
In CW's mind, the separation theory is his plan and he just wants to get on with it, he can't wait, and doesn't realise how strange he sounds.
Likewise when he's at the Thayers and starts talking about putting the house on the market. That's the next stage of his plan that he'd just like to get on with. Psychologically he's way ahead of everyone, since they don't even know she's dead at this point. He's come to terms with it already and is looking beyond. He also shows no interest in any of the Thayers ideas of where they could look for her. It's pointless to him, he knows where she is.
It reminds me of Gerard Baden-Clay, when his wife's body was found about eleven days after she went missing, he filed paperwork for her life insurance the same day. Who does that? Someone who has planned this all along and is just moving onto the next step of his plan. He knew she was dead all along, why wait any longer.
Scott Petersons wife goes missing and he adds the *advertiser censored* channel to his cable package.
They're over the loss of their families already, and find it frustrating that everyone else is so behind and making such a big deal about it. A few searches, a few memorial services, and they can just get on with their lives as they planned. Hurry up everyone..