Obviously none of the existing laws or rules prevented this tragedy. However, the prohibition of guns on campus did insure that no one else could have a gun to defend themselves. This is a fundamental fallacy with laws that prohibit concealed carry. Law-abiding people will obey such laws, but criminals and lunatics who are hell-bent on destruction will not. That leaves the lunatics armed while their innocent victims are unarmed and unable to defend themselves. But that in it’s self should not be the solution to such problems.
A situation like this should never have arisen in the first place. The background check system should have prevented the sale of a gun to someone who was way past disturbed. Beyond that the mental health system perhaps should have placed him in an institution. Even without guns he could have been dangerous. In 1990 another lunatic killed 87 people in New York using a can of gas and a match as his weapons. Certainly keeping homicidal maniacs off the street is a valid function of government.
At this point it seems unclear whether the instant check system has a glitch in it or whether something just went wrong in this case which allowed an insane person to buy a gun. In either event that should get corrected.
Obviously this is one reason why we should go back to the old system of the state
forcing the mentally deranged into state run mental institutions.