My bet is the thief pulled a gun when confronted by the owner.
Don't care. If you steal property, you deserve death.
Just say “You are putting me in fear of my life...” and shoot until he can no longer pose a threat.
Even if alone, chant. Someone might be listening or he might have his phone on. Say it, mean it, and shoot until no longer necessary.
That you stalked him is irrelevant.