Exhibiting completely different behavior to produce completely different pyschological evaluations, and a whole decade meticulously planning the worst shooting massacre in history, while carefully avoiding anything that might draw police attention, demonstrate that. Unless he gets Alzheimers or something, he will never lose that capacity, and has shown he can conceal both the ability and intent for the entire period he is ineligible for parole. He did not just snap one day and start shooting; he spent ten years of detailed planning and equipping for the "perfect" killing spree, going out of his way to avoid all suspicion throughout that time. There is simply no way he can prove he is not still doing the same thing right now, and never will be.