This is weird to me, 'challenge to disprove self defense' - since the accused was retreating towards law enforcement, and in general you have a duty to retreat if possible, I don't quite get the leap necessary that the pistol wielder was scared for their life. I can, however, believe that post-incident introspection would color the encounter this way, to the person with the pistol.

If there's an active shooter the general thing to do is hide, not go after anyone that is carrying a weapon.

I don't think there's a snowball's chance that any verdict will be accepted as is, though. I know most of my acquaintances have already made up their minds, trial outcome be damned.