If he had stayed in his car and allowed the police to handle it, he wouldn't be sitting in a courtroom today. Instead, he confronts an innocent person. His comments on the 911 call leads me to believe he thought he was a criminal. You don't confront criminals nicely. His comments on the phone also makes it highly believable that he would try to unlawfully detain him (They always get away with this stuff.) Martin knew he was being followed by some stranger.
Innocent guy confronted by some stranger who believes he's some criminal thug.
Usually doesn't end well.
Stranger who's in the wrong place (should have been in his car waiting for the police) confronts innocent guy minding his own business. Fight breaks out, confronter gets whooped. Shoots and kills guy. Claims self defense.
Had he stayed in the car instead of trying to play cops and robbers, no one would be dead.
His reckless actions ended in him killing a guy that was minding his own business. I call that murder.