What I keep coming back to is this..
EVEN if Karen hit him, I don't think she did it intentionally and I don't believe she knew she did it so she didn't hit him and drive away to leave him to die.
What is really clear regardless of whether she hit him or not is the police did NOT do a good job. Some key players here are lying, deleting and hiding things and that leaves me questioning WHY? Something really off is going on with the family that lived in that house where he was found. It isn't just one or two things and with so much going on that was not on the up and up, I don't see how EVERYONE isn't wondering what the heck actually happened that night. Why is there a LEO inside that house and he didn't come outside and why was the sister of one of the homeowners NOT worried about her sister and family inside that house when they discovered a dead man on the lawn?