Via the WSJ:
The bucolic campus of Virginia Tech, in Blacksburg, Va., would seem to have little in common with the Trolley Square shopping mall in Salt Lake City. Yet both share an important characteristic, common to the site of almost every other notorious mass murder in recent years: They are "gun-free zones."
Forty American states now have "shall issue" or similar laws, by which officials issue a pistol carry permit upon request to any adult who passes a background check and (in most states) a safety class. Research by Carlisle Moody of the College of William and Mary, and others, suggests that these laws provide law-abiding citizens some protection against violent crime. But in many states there are certain places, especially schools, set aside as off-limits for guns. In Virginia, universities aren't "gun-free zones" by statute, but college officials are allowed to impose anti-gun rules. The result is that mass murderers know where they can commit their crimes.
Private property owners also have the right to prohibit lawful gun possession. And some shopping malls have adopted anti-gun rules. Trolley Square was one, as announced by an unequivocal sign, "No weapons allowed on Trolley Square property."
In February of this year a young man walked past the sign prohibiting him from carrying a gun on the premises and began shooting people who moments earlier were leisurely shopping at Trolley Square. He killed five.
Fortunately, someone else -- off-duty Ogden, Utah, police officer Kenneth Hammond -- also did not comply with the mall's rules. After hearing "popping" sounds, Mr. Hammond investigated and immediately opened fire on the gunman. With his aggressive response, Mr. Hammond prevented other innocent bystanders from getting hurt. He bought time for the local police to respond, while stopping the gunman from hunting down other victims.
At Virginia Tech's sprawling campus in southwestern Va., the local police arrived at the engineering building a few minutes after the start of the murder spree, and after a few critical minutes, broke through the doors that Cho Seung-Hui had apparently chained shut. From what we know now, Cho committed suicide when he realized he'd soon be confronted by the police. But by then, 30 people had been murdered.