Not that there's anything to laugh about, but it's comical...him thinking he could plan a story of SW and the kids perhaps leaving and just disappearing and him not having "any inclination" of where they went when there was a camera pointing at his house the whole time. I have to believe they got into an argument and this was a crime of passion/ rage. He killed the children after SW as part of the cover.
Other than that, maybe he killed CeCe accidentally/or in a rage, and killed the other two to try and cover for it. I say this because of what he initially said about CeCe in the first couple of interviews. Plus, the reports of him crying when CeCe was named in court when he was giving his guilty plea. There's something to that.
3rd scenario, in short, he killed them to be free. How ironic.