...I have the impression that a gonne could kill any of us quite easily, powers or not. Perhaps Bernkastel could have done something with probability to make the weapon break, but magic hair, unlocking doors, even flying and creating shuriken - none of that is quite as effective, is it?

If the murderer got ahold of the gonne prior to the murder - Gundam included - they might not have felt a need to nullify his abilities. They were very unclear in the first place.