If I were on the jury, I'd be thinking he's guilty as sin. In law, in the absence of any other reasonable conclusion you have to go with the one being offered. We've not heard his version yet but from what we can glean from the sons evidence it appears he's belatedly clutched at a straw so thin and flimsy it will break under the tiniest bit of scrutiny.
To a normal person, his actions make little sense. But if you view his actions through the prism of a person with an APD everything fits. I have no doubt of his guilt and I suspect by the end of the trial most people will be aghast at how a seemingly, passive, affable, guy could fool so many for so long. The truth is prisons and psychiatric hospitals are full of such people.
Some have a litany of offences and conduct disorder from a young age and nobody is surprised when the end up incarcerated. Other highly functioning, highly intelligent, persons with psychopathy manage to hide their condition all their lives. Somewhere in the middle of these two extremes lay the Ian Stewart's of this world.
What makes such predators so dangerous is because they can detect a victim just by watching the way a stranger walks whereas their prey and others like their prey cannot begin to comprehend or rationalise such evil because it is, and always will be, alien to them. Those with anti social personality disorders use this to their advantage.