doesn't sound like any 3rd party witnesses around
He was caught because another passenger of his boat turned him in the next morning so there is an eye witness. He was being asked to plea to "criminally negligent
homicide" which is death due to exceptionally stupid behavior plus leaving the scene. They never said he tried to kill him. That is a pretty fair plea bargain. The judge was even willing to let him serve the charges concurrently.
wanted to cut a deal without jail time but the judge won't hear it. So they go around and around until he pleads knowing he gets jail time or they hold out for a grand jury indictment. The jury would clearly send it to trial that is of no doubt. What charges they may throw at him are unknown and of course the judge won't see the case the same way if it goes to trial and he loses.