One would think the mother would consider the negative consequneces to her son of having his father suffer the consequences for the son's actions.
His life could be ruined by the guilt and the inner conflict and the mother has to know that!
David's life is ruined regardless of the outcome of the trial.
About the mother, it was just something that I heard, I believe it originally came from a radio report in SD. Who knows if it's even true. Go figger.