Whether or not this verdict is just depends on the law in Colorado. Does Colorado law allow deadly force to protect property? If it does, then the property owner was acting within the law, and the family should have had no case. If Colorado law does not allow deadly force to protect property, then the property owner (in addition to the thug) broke the law, making him potentially criminally and civilly liable for the death of the thug.
Legal or not, I would not have shot in that circumstance. I would have attempted to hold the thugs for the police, in the full realization that such may have proved vain if I were not willing to shoot until and unless life or limb were in imminent danger.