Dozens of people gathered for a vigil on the 20th anniversary of the Columbine High School massacre, laying flowers at a memorial for the victims.
Twelve students and a teacher were killed on April 20, 1999, when two teenagers armed with an assortment of weapons and home-made bombs went on the rampage at the school, whose name has become synonymous with school shootings.
There have been more than a dozen other shootings at schools across the US since Columbine.
Only last year, 17 students and staff were killed when an ex-pupil went on the rampage at Marjory Stoneman Douglas High School in Florida, while 27 people, mostly children, were killed at Sandy Hook elementary school in 2012 and 32 at Virginia Tech University in 2007.
On Friday, survivors of the Columbine massacre and families and friends of the victims gathered in Littleton, Colorado.
They lit candles and prayed at a memorial in the town, and laid flowers on plaques bearing the names of victims.
An inner circular wall bears biographies of the victims carved into marble, while an outer wall lists those injured in the attack.
“Never forget” is carved in stone on the floor.
Speaking earlier this week, survivor Amanda Duran expressed anger that school shootings were still taking place.
“You would have thought someone would have come with more gun laws or require (a) mental health workout before you are allowed to buy a gun,” said Duran, who was 15 when the attack happened.
“But nothing of that sort happened. So I have just been angry and pissed off.”
The aftermath of Columbine is still felt.
An American teenager whose obsession with the massacre set off school closures and a manhunt in Denver was found dead on Wednesday from an apparently self-inflicted gunshot wound.
Dean Phillips, the special agent in charge of the FBI’s Denver office, said 18-year-old Sol Pais had made comments in the past that expressed “an infatuation” with the Columbine massacre and its perpetrators.
Authorities had mounted a massive search for Pais after she traveled from Florida to Colorado, bought a pump-action shotgun and ammunition.
Colorado authorities, who said Pais was armed and considered “extremely dangerous,” had ordered around half a million students to stay at home “due to ongoing safety concerns.”