At a press conference in response to last week's tragic Sandy Hook shootings, the National Rifle Association called on Congress to put armed police officers in every school in America.

The logic is simple — trained officers in possession of firearms would be able to neutralize those seeking to murder students.

However, a number of recent shootings call this logic into question. Immediately after the NRA press conference, anti-gun group Violence Policy Center released a statement pointing out that at the deadly gun attack at Columbine High School there were two armed officers on campus.

The officers were apparently outgunned by the two teenagers*. A police transcript included by VPC reads:

[Jefferson County Sheriff’s Deputy Neil] Gardner [the school’s community resource officer], seeing Harris working with his gun, leaned over the top of the car and fired four shots. He was 60 yards from the gunman. Harris spun hard to the right and Gardner momentarily thought he had hit him. Seconds later, Harris began shooting again at the deputy. After the exchange of gunfire, Harris ran back into the building. Gardner was able to get on the police radio and called for assistance from other Sheriff’s units. “Shots in the building. I need someone in the south lot with me.”

In 2000 CNN published a detailed account of Gardner's response during the shooting. The sense of chaos is remarkable.

Virginia Tech, the site of the deadliest U.S. gun massacre ever committed by one person, has a police department on the grounds. According to the AP, the shootings in that incident took place over just 9 minutes — it took the campus police 3 minutes to reach the building, and five minutes to break into the building, which had been locked by the gunman.

At the Colorado cinema shootings earlier this year, it took police officers just 90 seconds to get to the scene of the shooting, but 70 people had already been shot; 12 fatally.

These incidents show that a "good guy with a gun" — in the words of NRA CEO Wayne LaPierre — can often do little to stop a well-armed intruder intent on creating chaos and willing to die.

Putting a cop in every school would also be much more expensive than a plan that bans or limits availability of deadly weapons.

Think banning assault weapons is the answer? Watch the video below to see what the 1994 Federal Assault Weapons Ban did.

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*The original draft of this article said the Columbine attackers were using "assault weapons", as per the VPC press release. A look at their weaponry suggests they were not using guns that would be classed by assault weapons, and this has been removed.