Soldato
He wasn't chased down. One man walked towards his person space and maybe reached towards his weapon. Whether that's self defense or not will be a contentious argument.
And oh okay, it's okay to shoot a random person because you heard a shot somewhere
Joseph Rosenbaum wanted a fight (see footage of him squaring up to the armed guys earlier in the evening) and tried to take his weapon, very very stupid. And the world has lost nothing of value.