Hans Reiser was found guilty of first degree murder. However, his prosecutor agreed to a plea deal with him of second degree murder after this conviction, on the condition that Reiser reveal the location of his murdered wife's body.
I understand why a prosecutor would accept a plea deal for a lesser crime in place of slogging through a trial for a chance of a conviction on a greater crime, but I do not understand why the prosecutor would want to accept such a plea deal after already having scored the conviction of the greater crime. I find it hard to believe that a state prosecutor would particularly care whether the body could be found or not after the associated conviction and already been scored.