Americans' fears over the safety of schools continues.

Last Monday, three colleges and four K-to-12 schools were shut down by threats of violence.

This week over 25,000 college students at 300 chapters in 44 states belong to a group, Students for Concealed Carry on College Campuses, that will carry empty handgun holsters to protest their concerns about not being able to defend themselves.

With the first anniversary of the Virginia Tech attack last week and the discussions that it created, we clearly have not been able to put that and other attacks behind us. There are good reasons why the safety measures adopted over the last year to speed up response times or hiring more police haven't eliminated the fear people feel.

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The attack earlier this year at Northern Illinois University proved that even six minutes was too long. It took six minutes before the police were able to enter the classroom, and in that short time five people were murdered. Compared to the Virginia Tech and other attacks, six minutes is actually record-breaking speed, but it was simply not fast enough.

The Thursday before the NIU murders five people were killed in a city council chambers in Kirkwood, Mo. There was even a police officer already there when the attack occurred. But as happens time after time in these attacks, when uniformed police are there, the killers either wait for the police to leave the area or they are the first people killed. In Kirkwood, the police officer was killed immediately when the attack started. People cowered or were reduced to futilely throwing chairs at the killer.

There is a problem that people just are unwilling to recognize.

Just like attacks last year at the Westroads Mall in Omaha, Neb., or Trolley Square Mall in Salt Lake City or the recent attack at the Tinley Park Mall in Illinois or all the public schools attacks, all these cases had one thing in common: They took place in “gun free zones,” where private citizens were not allowed to carry their guns with them.

The malls in Omaha and Salt Lake City were in states that let people carry concealed handguns, but private property owners are allowed to post signs banning guns and those malls were among the few places in their states that chose to post such signs. In the Trolley Square attack an off-duty police officer fortunately violated the ban and stopped the attack. The attacks at Virginia Tech or the other public schools occurred in some of the few areas within their states that people are not allowed to carry concealed handguns.

It is not just recent killings that are occurring in these gun-free zones. Multiple-victim public shootings keep on occurring in places where guns are banned. Nor are these horrible incidents limited to just gun-free zones in the US.

In 1996 Martin Bryant killed 35 people at Port Arthur in Tasmania, Australia. In the last half-dozen years, European countries including France, Germany and Switzerland have experienced multiple-victim shootings. The worst school attack in Germany claimed 17 deaths, another 14 deaths; one attack in Switzerland claimed the lives of 14 regional legislators.

At some point you would think that something is going on here, that these murderers aren’t just picking their targets at random. Yet, when one thinks about it, this pattern isn’t really too surprising.

Most people understand that guns deter criminals. The problem is that instead of gun-free zones making it safe for potential victims, they make it safe for criminals.

Criminals are less likely to run into those who might be able to stop them. Everyone wants to keep guns away from criminals, but the problem is who is more likely to obey the law.

A student expelled for violating a gun-free zone at a college is extremely unlikely ever to get into another college. A faculty member fired for a firearms violation will find it virtually impossible to get another academic position. But even if the killer at Virginia Tech had lived, the notion that the threat of expulsion would have deterred the attacker when he would have already faced 32 death penalties or at least 32 life sentences seems silly.

Letting civilians have permitted concealed handguns limits the damage from attacks. A major factor in determining how many people are harmed by these killers is the amount of time that elapses between when the attack starts and when someone with a gun is able to arrive on the scene.

In cases from the church shooting in Colorado Springs, Colo., last December, where a parishioner who was given permission by the minister to carry her concealed gun into the church quickly stopped the murderer, to an attack last year in downtown Memphis, to the Appalachian Law School, to high schools in such places as Pearl, Miss., concealed handgun permit holders have stopped attacks well before uniformed police could possibly have arrived.

Twice this year armed Israeli citizens have stopped terrorist attacks at schools (once by an armed teacher and another by an armed student). Indeed, despite the fears being discussed about the risks of concealed handgun permit holders, I haven’t found one multiple-victim public shooting where a permit holder has accidentally shot a bystander.

With about 5 million Americans currently with concealed handgun permits in the U.S. and states starting having right-to-carry laws for as long as 80 years, we have a lot of experience with these laws, and one thing is very clear: Concealed handgun permit holders are extremely law-abiding and lose their permits for any gun-related violation at hundredths or thousandths of one percentage point. We also have a lot of experience with permitted concealed handguns in schools.

Prior to the 1995 Safe School Zone Act, states with right-to-carry laws let teachers or others carry concealed handguns at school, and several states still allow this today. And there is not a single instance that I or others have found where this produced a single problem. There are today even some universities, including large public universities such as Colorado State University and the University of Utah, that let students carry concealed handguns on school property.

With all the news media coverage of the types of guns used and how the criminal obtained the gun, at some point the news media might begin to mention the one common feature of these attacks: they keep occurring in gun-free zones.

Gun-free zones are a magnet for these attacks. But, even without the media, considering that 15 more states this year debated legislation to let concealed handguns on school campuses, possibly the issue is becoming clear anyway.