If this is the standard, then what should happen to the property owner if he shoots an alleged thief, and it's discovered later that the property owner was mistaken?
This gets back to Modelworks' point: If you make it legal to shoot at someone who's trying to abscond with your property, you create a pretext for shooting at anyone.
Since there's no death penalty for theft, how can shooting at an escaping thief possibly be justified?
Bolded for a WHAT THE FUCK comment. Seriously I mean what the fuck are you stating here. Do you know how absurd that sounds? No it does NOT create a pretext for shooting at anyone. All it creates a pretext for, and get this for real causation, is for allowing people to defend their person, loved ones, home, and property with lethal force if necessary against people perpetrating a crime against them.
What you did there was a huge example of logical fallacy by division.
http://en.wikipedia.org/wiki/Logical_fallacy
As for no death penalty for theft. Are you that stupid? Sure most of the laws are old but there are US laws that the maximum penalty for is death in regards to theft. Hell, Colorado STILL has on it's book the anti horse theft law where the maximum penalty is... get this.. death! Just because the death penalty is never used anymore for theft related crimes does not mean the penalty is not there among various laws.
As for courts now not using capital punishment in the US, that is because they typically know most or all the facts of the case by the time sentencing is occurring. Meaning by the time a criminal winds up at court, if theft was the only real motivation, then there are ways for the victim to receive reprisal from the criminal without the need for capital punishment.
In the case of someone defending them self and other their property, the person at the actual time of the crime has NO IDEA what the criminal intends to do. Why? because they are doing it that very moment. The 82 year old guy has no idea if the criminals intended to drag off his trailer and then circle back around and use their vehicle now with EXTRA MASS from the trailer as a battering ram to take him and or his house out. While the crime is happening, the victim has no clue what the final outcome is or what the criminal intends to do. As such, killing a criminal in that case is not the same thing as a court sentencing for capital punishment.