This phenomenon has been recurring since the first such incident at Moses Lake, Oregon, in 1992. No gun control law would have prevented people with absolutely no moral restraints and absolutely no sense of self-preservation from committing these crimes. Public schools often have captive clienteles, especially in inner cities, and they know it. Just as important, private schools also have more freedom to experiment. In private schools, disciplinary policies aren't civil liberties issues.
Private schools get to have private rules.
And freedom also means freedom to carry out grander experiments that would be unheard of in the public sector. They had also planted bombs, which failed to detonate. Because they rightly realize that behind these 'reasonable restrictions' lurks the desire of many people to ban guns outright. But even if guns were totally banned, this crime still wouldn't have been prevented. Sometimes trying to ban certain behavior, even out of the best of intentions, does more harm than good.