He did that.
The circumstances did not let him enough time to react and most likely he did not have anything else but his gun. Who knows what Martin him to make George leave his car. But it's obvious he did NOT leave this car to kill Martin.
He could have done many other things as in what? Beat him up? Because Martin would not back up like that. The kid was a punk. Did he deserve to die? NO! Could George do anything else? Maybe. Did he? NO!
Is he "innocent"? Yes and no. Did he kill a person? Yes. Was it in self defense? Yes.

