You can't shoot someone who is not aggressing you. Period. How hard is that? Imagine the following dialog, you in the witness chair. Except your lawyer would NEVER let you testify in this case. I truly hope the OP was a joke.
Prosecutor: So tell me again what you were thinking when you pulled the trigger?
You: well, he had my guns, my car, he had to die.
P: So, were you at any time afraid for your life, or for someone elses?
You: No. Well, he might have taken my guns and shot someone else.
P: Did the decedent point a gun at you? Threaten you? Threaten your friend or family?
You: No
P: So there was no IMMINENT THREAT. Did the decedent have the ability to harm you?
You: i don't know. i only saw someone racing away in my car.
P: So for all you knew, he might have been a pregnant woman?
You: i didn't see him.
P; Did he aim the car at you? Try to run you down? Display the ABILITY, INTENT or OPPORTUNITY to harm you in any way?
You: no.
P: And you shot him anyway?
You: Well, he had my car and my guns.
P: So you gunned him down? shot him in the back? Did you think what might happen to bystanders if you missed, or if he crashed his car into the drugstore?
You: No, he had my guns and my car.
P: So, basically you didn't think. You just made a great shot.
You: Yeah! It was wasn't it - moving target, from more than 30 yards, headshot (Boom) DRT.Wish he hadn't bled out all over my car though.
P: The Prosecution rests, your honor.