I wonder how premeditated this all was. Did he say, I am going to kill my child and then stage it to look like an accident? If he did, it shows major entitlement issues that he thought this would be a great coverup. He is probably used to people liking him, and did not think that anyone would buy that a great guy like him could kill his kid.
But could it be more impulsive and not really thought out?
Well, I think he thought about it all day at work. Whether it was planned before hand, or a reaction to something that happened that morning...we won't know for some time I guess. I kind of assume that it was such a bad cover up, because he was thinking about how to pull it off all day at work, in a frantic psychological state.