South Dakota Republican Attorney General Attorney General hit/killed what he says he thought was a deer. Why didn't he stop to investigate?

What he hit and killed was a man.

Background on the killer

Six speeding tickets in six years
Was driving home from a Republican Fundraiser.  He attends MANY REPUBLICAN FUNDRAISERS. WAS HE DRUNk?

Isn't it ILLEGAL to hit something and not stop to investigate?