Exactly What "Stronger Controls" Would Those Be?

A New York Times editorial about the Virginia Tech mass murder states, "What is needed, urgently, is stronger controls over the lethal weapons that cause such wasteful carnage and such unbearable loss." My question, now that we have a little more information about the criminal (though I stress far from complete information): What stronger controls over weapons would likely have stopped him from committing the murders, or even led him to kill fewer people?

Note that I'm not asking what controls would have prohibited him from doing something. Murder law, and for that matter the gun control law that banned firearms from campus, already prohibited him from committing mass murder. That didn't seem to help. I'm curious what "stronger controls" would likely have stopped a would-be mass murderer from killing, or at least killing as many.