The thing is, only he can reveal the motive, but would you believe him?. He has managed to look people in the eye for a month, holding on to a secret the whole town was talking about and organising searches, and food and drinks and accommodation for the searchers, the little village full of coppers, and sniffer dogs and what not. Yet he fooled them all. So he could look you in the eye too, and tell you a motive. Any motive.
I am sure he is , as I type here looking over my balcony, thinking up a credible motive. One that his barrister can use in court.. Did he have a reason ? probably. One that satisfied him at the time. Possibly he does not remember exactly what that reason was now, since the urgency has passed . People can, and probably will ascribe motives to him, but they would be meaningless without his input, yet his input is severely tainted by his dire circumstances...