I was trying to say that if the guard stayed in his car, it would have offered a security blanket of protection to his position on the scene. In the event the thief did have a weapon like a knife, etc...the steel body offers an extra degree of protection to allow a defensive or offensive move, whether that move was using the car as a weapon in order to end the threat to his life or not. I'm not advocating using the car over another weapon like a pistol, but it's merely an option that one has to recognize as part of a given reality, from the limited facts that we're given. Under the circumstances, maybe a jury would be more sympathetic to the use of the car as a weapon than even a firearm.
What seems to be misunderstood by my initial argument is not that there is anything wrong with using lethal force against a reasonably perceived threat to one's life, but rather one should not use any deadly force unnecessarily just for the sake of the recovery or protection of property, especially if it has already been taken off of your property. After all, irrespective of any particular or peculiar state law, the average person in just about every state could end up facing a trial, prison or both.
Intent is 99% of the law, and if the pure intent of the shooter is not to end the perceived "reasonable" threat to one's life, then it may not matter what the jury believes, the prosecutor will do his job and one's life could be left in ruins, win or lose!
Am I against using a firearm or other weapon against a real and reasonable threat? No, of course not, but simply stealing property and fleeing the scene does not necessarily constitute a threat.
Usually police can more readily avoid the threat of prosecution for doing the job that they were trained to do because of their extensive training and reputability.
It's often better to be safe than sorry, and I have a hard time believing that the car thief in this instance was just joy riding while the guard followed him. But those facts are missing and witness statements may not yet be available to the public.
It's not a good thing to promote and reinforce a Yahooistic revenge motive of this sort when most states have laws, prosecutors and a citizenry that by and large, just won't support it.