I actually have no problem with shooting a fleeing violent armed perpetrator. He is not just fleeing from his current crime, he is fleeing to his next crime where his victim(s) might not fare as well.
I carefully read chapter 9 of the Texas Penal Code with deals with justification including all of the defense of self, others, property etc. There isn't anything that would justify a civilian shooting a fleeing felon unless the civilian did so in the presence and at the direction of a police officer.
I don't know about Colorado law, but in Texas if someone is running away you can't shoot him because he is running towards his next crime.