Double Naught,
Given that the person is apparently face down on the ground makes for even LESS reason to shoot him in the back.
Once he began to flee, his status remains fleeing unless he reverses course and attempts to re-engage the other individual in the altercation, or attempts to engage another person in a hostile act.
But, once he hit the ground, it's also very likely that he was helpless. Granted, you and I both know that, from what we've read, it's no big deal that this scumbag was helpless.
But in our legal system everyone theoretically has the same rights (yeah, I know, don't choke laughing
), and the system tends to take a pretty dim view of shooting someone in the back when they're down, unless they're posing an IMMEDIATE threat, not a potential or perceived threat.
As for the specific references that it is illegal to shoot someone in the back, I don't think there is such a citation under Virginia law.
Why? Because it's NOT illegal to shoot someone in the back if he/she poses an immediate, grave threat to someone else.
So much of our law comes down to interpretation, intent, and condition.
That's why self-defense laws have language such as "reasonable belief that you are in grave danger" or "reasonable belief that someone else is in grave danger."
No law can be written to cover all SPECIFIC instances or events. What the intent is, though, is that the law be both specific AND general, so that the spirit of the law can be interpreted by the attorneys, courts, and juries.