If the owner is a 'canine heart specialist' and the dog was allegedly hit hard enough in the head to render it unconscious, did they take it to a vet between the time of the incident and 5 days later when the dog died? Because that's a pretty big 'yikes!' if they didn't.
Also, totally agree with what's being said here. They didn't see what happened because the dog was behind the owner. They have no idea what actually happened. I also think it would be wild for someone to kick a 60+ lb lab and ride on by like nothing happened.