I've been very clear in saying I think they had a duty to stop and stay with him, even if they couldn't save him.
But I'm equally clear that it's a moral failure, not murder. They didn't kill him. There's no reason to believe they could have saved him. Their failure was moral, not legal, and it wasn't murder, but lack of compassion.
Where there's life, there's hope. These people were too absorbed in their own little self interests to be concerned with the life of another. When they walked away from this guy--they murdered him. It doesn't matter if the guy would have died anyway, who will know this now?
The fact is, they willfully walked away from another human in dire need. This guy might as well have been in a concentration camp--no reason to risk my neck trying to save him, he's dead anyway.