I think the bigger question is this:
If this child had a gift taken for behavior issues and his response was to sneak to find it AND, when he did not, he leapt to shooting his father, the disordered thinking is not predictable and no way near proportional. One could argue that an 11 year old is not fully developed. One could further argue that he was not recognizing the consequences of his actions. Apparently, neither parent thought that he would stew on this the way he did. Further neither parent thought he was capable of the heinous action he committed. The family friend describe escalating behavior that made the family fear for the safety of other children at school-- requesting a class change.
Even with amazing therapy and eagle-eye supervision, a person with this profile can be a ticking time bomb. When can you say he is trustworthy and the situation is safe? Is it possible that he can learn perspective taking and understand the results of his behavioral choices/actions? How many feet do you stand away from them when other vulnerable people are in the area? What is the right amount of risk? Tackles happen in an instant. Slamming a head into a concrete wall can be fatal. A push into traffic or out of a window. An attempted drowning in a toilet. A finger gouging out an eye. A metal chair that hits a head. I have witnessed all of the above in my line of work. AND, I have seen been totally surprised at the young people who have done these actions-- did I think it was possible? Yes, but I never would have imagined that it would become a reality. I thank the heavens that my students didn't succeed at killing but I am totally sure if they had not been stopped that a killing might have been a result. Additionally, any number of my students would feel bad about their actions in retrospect but would continue chew on it until they get back to feeling justified. These disorders can morph into anti-social disorders of scary magnitudes with small actions.
The threat here may have a chance to be mediated and he can be taught to deal with frustration and anger. That said, can he ever be seen as safe? If we look at the Slender Man attackers (young girls who attacked another unsuspecting young girl) we have seen at least one on the precipice of being free AND making an outrageous choice to runaway because she feared the group home would limit her from being with the man she was interested in. This woman was on track to be released--- no ability to not have what she wanted even to the point where she screwed herself becoming free.