Ten years on, and the name Columbine is still synonymous with the worst mass school shooting in American history.
The names of the victims are engraved on the Columbine memorial
The library where the two disturbed teenagers, Eric Harris and Dylan Klebold, roamed and fired indiscriminately has now been rebuilt.
But as you enter, you can still imagine the sheer terror as their victims tried to hide behind and under the desks.
Now, engraved in stone on the library wall, are the names of the 13 murdered by Harris and Klebold.
Among their victims was Daniel Mauser - just 15 years old. For the past decade, his father Tom has been campaigning for tighter gun controls. He has had limited success.
He says he sometimes feels as if his son were "collateral damage" - the price paid for America's freedom and liberty.
I think the real reason why the public should have semi-automatic and fully automatic weapons is to protect themselves from the government
Gun shop customer
But he says with rights come responsibilities, adding: "We've shown a really irresponsible attitude to firearms in this country."
The evidence for that, of course, is not just Columbine.
A few days ago, the students at Virginia Tech were marking the second anniversary of the murder of 32 people by a lone gunman. And there have been a series of mass shootings just this month.
The Brady Campaign - a US group that lobbies for stricter controls - says that every day in America 32 people die in shootings.
Columbine may have sparked a national debate about gun control, but the debate has not really moved on.
It is not much harder to buy a gun now than it was a decade ago - in fact in some states it is easier.
In Virginia, you can still go to a gunshow and buy a weapon without any kind of check.
At Firing Line - Denver's largest gun store - they are doing a roaring trade, even though the country is caught in the middle of an economic downturn.
Students and staff mark the anniversary of the Columbine massacre
Stocks of some rifles are running out and ammunition is being rationed.
Richard Taylor, the store's manager, calls it the President's Inventory Sale - in honour of Barack Obama.
He says demand has rocketed since Mr Obama was elected, as a consequence of the widespread fear that the new president will introduce tougher laws. There is, Mr Taylor says, no recesion in the firearms business.
There is plenty of anecdotal evidence to back up this theory, but the FBI criminal background checks - required before you can buy a gun - gives the best statistic: since Barack Obama's election, the number of checks being carried out has risen by almost 30%.
Battle too far
Brendan and his girlfriend Oona are among the large crowd of customers at Firing Line. He says he already owns around 100 guns and this time he has got his eye on a semi-automatic rifle.
I asked Brendan why he needed another weapon.
At first he said the model he was considering would be good to shoot at coyotes.
RECENT US SHOOTINGS
A gunman kills 13 people at an immigration srevices centre in Binghamton, New York
A gunman kills a total of 11 people in a series of shootings southern Alabama
A gunman dressed as Santa Claus kills nine people and himself on Christmas Eve in LA
Six people die in a series of shootings in the north-west of Washington state
A worker at a plastics plant in Kentucky kills five people before killing himself
32 people and the gunman die at the Virginia Tech campus
Then, after a pause, he added this bombshell: "To be honest, I think the real reason why the public should have semi-automatic and fully automatic weapons is to protect themselves from the government".
Unabashed, he adds: "I know that's going to sound right-wing."
But America's love affair with the gun crosses the political divide. There are Democrats who are just as passionate.
Another customer, Reed, repeats the line "out of my cold, dead hands" when I ask how he would respond to stricter controls or any attempt to outlaw some weapons.
And if you remind gun owners of Columbine, they will repeat the familiar refrain that it is "people who kill people, not guns".
The reality is that President Obama has so far shown little appetite for taking on this powerful lobby.
He got burnt in the election campaign when he talked dismissively of the people who "cling to guns and religion".
With so much else on his plate right now, gun control seems to be a battle too far.
For millions, guns are part of the American way of life.
The Second Amendment - the right to bear arms - is not just written into the constitution. It is ingrained in their psyche.
And it would be a very brave man indeed who tried to re-interpret that right, whatever the tragedies guns have caused.
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