Joe Horn walked in 2007 for killing two men under similar circumstances. But I think California does take a dimmer view of this.
Also Horn shot them on his property, not in a common area.
And Horn told them that he would not shoot them if they stayed put for the police - they were not unarmed and begging for their lives.
Horn also called 911.
Another possible factor: a plainclothes cop was on the scene at Horn's and did not identify himself - I believe the reasoning was that he was afraid that something might happen to Horn if he announced himself and confused the situation before uniforms arrived.
Pretty thin stuff, and no-billing Horn probably prevented further inquiry into this aspect.