Honestly, proper gun control would mean that someone with that diagnosis completely loses access to guns - and yes, that means that his own guns should have been confiscated.

However, we get this after every mass shooting: people say that it's not guns, it's a mental health issue. But as soon as concrete measures are suggested that would keep guns out of the hands of someone who's mentally unstable, those same people will yell at you "SHaLl NoT bE InFRinGeD!!1!1!!"