In watching his porch interviews, I thought he came off as a pretty smooth liar when he thought he was in control of the interviews. He looked straight at the camera when he lied and he didn't flinch.
I think what really messed him up in the interviews is primarily two things. First, he had to play two separate and conflicting roles in those interviews. One role was for LE and the public and that was of being a concerned husband and father. The other role was for NK's benefit and he barely referred to his missing wife and children by their names, didn't mention Shanann's pregnancy, said weird things like "it's vanished", and he smiled and chuckled inappropriately. I think those chuckles and smiles were for NK - as in "I told you Shanann was crazy".
The other problem he had was motor mouth. He couldn't explain how Shanann and the girls left the house so he went on and on and he was stumbling badly.
Marlon Brando would not have been able to pull off two such conflicting roles at the same time, but CW thought he could and he did three separate interviews. He's so narcissistic, self-absorbed, and completely lacking in self awareness that he had no clue that others, and LE would view his interviews as evidence of guilt. He probably thought he did a good job in the interviews until one of his friends told him otherwise.
JMO, CW is far from smart. Smart people don't do things that will land them in prison with the death penalty or LWOP, but psychopaths do it all the time. They greatly overestimate their abilities and their own intelligence and they greatly underestimate the intelligence and abilities of others. They simply don't think there will be any consequences to pay.
JMO
I imagine he thinks he is a stable genius