I don't know how I would vote in such a case, because I don't know the applicable laws. In any event, how I FEEL about the case has no bearing. As a juror, it is my duty to find guilt or innocence based on the evidence and the law as it applies to the specific case.
The case as you describe it would appear to be civil, not criminal, and the legal standards and applicable statutes vary widely from jurisdiction to jurisdiction.
My personal view is that if the victim brings his gun onto the workplace property, so long as he keeps it securely stowed in the vehicle, that should be allowed, since I view the vehicle as an extension of sorts of the victim's property. The right to bear arms and the rights of property owners are both hot button issues for me, so its not an easy call.