[MarineHawk]

A little dated, but still valid:

Originally Posted by Prof. John Lott

Hardly mentioned in the massive news coverage of the school-related shootings during the past year is how they ended. Two of the four shootings were stopped by a citizen displaying a gun. In the October 1997 shooting spree at a high school in Pearl, Miss., which left two students dead, an assistant principal retrieved a gun from his car and physically immobilized the shooter while waiting for the police.

More recently, the school-related shooting in Edinboro, Pa., which left one teacher dead, was stopped only after a bystander pointed a shotgun at the shooter when he started to reload his gun. The police did not arrive for another 10 minutes.
Who knows how many lives were saved by these prompt responses?
Anecdotal stories are not sufficient to resolve this debate. Together with my colleague William Landes, I have compiled data on all the multiple-victim public shootings occurring in the U.S. from 1977 to 1995. Included were incidents where at least two people were killed or injured in a public place; to focus on the type of shooting seen in the Ferguson rampage, we excluded gang wars or shootings that were the byproduct of another crime, such as robbery. The U.S. averaged 21 such shootings annually, with an average of 1.8 people killed and 2.7 wounded in each one.
We examined a range of different gun laws, such as waiting periods as well as methods of deterrence, such as the death penalty. However, only one policy was found to reduce deaths and injuries from these shootings: allowing law-abiding citizens to carry concealed handguns. The effect of "shall-issue" concealed handgun laws, which give adults the right to carry concealed handguns if they do not have a criminal record or a history of significant mental illness, was dramatic. Thirty-one states now have such laws. When states passed them during the 19 years we studied, the number of multiple-victim public shootings declined by 84%. Deaths from these shootings plummeted on average by 90%, injuries by 82%. Higher arrest rates and increased use of the death penalty slightly reduced the incidence of these events, but we could not conclusively determine such an effect.

http://www.junkscience.com/news2/lott2.html

Another one:

Originally Posted by Massad Ayoob

A terrorist opens fire at a crowded bus stop; a passing Israeli motorist draws his 9mm pistol and cuts him down. A late-arriving security man with an M-16 hoses the twitching terrorist just to make sure.

Another terrorist attempts to trigger an explosive device in a public place. An Israeli housewife draws her pistol and shoots him dead before he can detonate the bomb. The would-be martyr dies alone.
A third terrorist opens fire with an automatic weapon in an Israeli school. What could have been a mass murder on the scale of Columbine or greater is limited to a very short casualty list when Israeli parents and grandparents, who have provided volunteer armed security after receiving state training, open fire and kill him with their concealed pistols.

Note that in each of these episodes, it was an armed citizen who stopped the terror. Not a soldier. Not a security guard. Not a police officer. Just as wolves do not try to seize a lamb under the nose of the sheepdog, terrorists do not strike where armed protectors are known to be present. They scout the turf and select their victims more carefully than that.

http://www.backwoodshome.com/articles2/ayoob81.html