In this particular case it should be pretty open and shut right? So what is the harm in letting the family determine the punishment? What the punishment won't fit the crime?
Forget everything else for a second and let's focus on this: Is there some provision in Colorado state law that allows the court to defer the verdict and or sentencing to the survivors and family members of victims when cases appear to be "open and shut" in the manner in which you are describing?
I'm acting under the assumption that no such provision exists and Colorado follows the same common model of judge and jury trials in place throughout the United States.