Albeit full justice was denied, the man pleaded guilty in what was in effect a plea bargain. Of course he was negligent. We don't need to know the "whole" story, the negligence and the post-negligence obfuscation say it all. If anyone thought they'd get so much as a unequivocal mea culpa from the guy, they don't know the Kennedy's.
Oh come on - he was with a single woman - driving off the main road to go to a deserted beach - had been at a party with 8 young single women and 8 married men - without their wives - and drives off a bridge where the young woman dies and doesn’t call the authorities until enough time as gone by for an alcohol test to be meaningless... yeah, no one will ever know... right.