I see.
On its own, that sounds less like murder and more like a citizen trying to detain a person behaving suspiciously in the neighbourhood, as he saw it. Using a camera to record the incident might be seen as a peaceful attempt to gather evidence for use later in a trial. In turn, that implies non-violent intent.
That would be the defence, and a robust one, unless there's evidence he was aware of the shooter's intent to use his firearm.
In terms of the shooter, this may be yet another case of the sheer awfulness of the second amendment in action.
Everyone is afraid of everyone else. So they shoot first and worry about the courts later. A good neighbour thinking he is keeping his neighbourhood safe becomes a gun-toting vigilante with murderous intent because he holds a weapon.
Justice is basically impossible when someone is permitted to hold a gun. The case would be open and shut if he wasn't. In fact, there would be no issue at all. The kid would either be alive or the shooter would clearly be a murderer. Instead, there's plenty of room for argument.
I think he may be done for manslaughter, but nothing more.