DENVER (KDVR) — “It brought the nation to its knees, but now that we’ve gotten back up how have things changed; what have we learned?” reads an inscription on the Columbine Memorial’s Wall of Healing.

On April 20, 1999, two students walked into Colorado’s Columbine High School and killed 12 students and one teacher, leaving over 20 other people injured. While history has chosen not to repeat the names of the shooters, the community knows the 13 victims will not be forgotten.

A quarter of a century later, the memories of those lost continue to be honored.

Those victims — Steven Curnow, 14; Daniel Mauser, 15; Daniel Lee Rohrbough, 15; Kelly Ann Fleming, 16; Matthew Kechter, 16; John Tomlin, 16; Kyle Albert Velasquez, 16; Cassie René Bernall, 17; Corey DePooter, 17; Rachel Joy Scott, 17; Isaiah Emon Shoels, 18; Lauren Townsend, 18; and William ‘Dave’ Sanders, 47 — were remembered Friday night at a vigil near the Colorado State Capitol.

At the vigil, small candles flickered on 13 empty chairs, and short biographies of the Columbine students were read one by one. After each, the attendees — including former Arizona Rep. Gabby Giffords, who was almost killed in a 2011 mass shooting — replied together “never forgotten” and a bell tolled.

Sanders’ daughter, Coni Sanders, said her father changed the world forever by saving hundreds of students.

“The kids that he saved now have children and those children will have children so generations from now people will know they exist because of his bravery,” she said before the ceremony began.

The gathering, set up by advocates including gun safety organizations, was the main public event marking Saturday’s anniversary, which is more subdued than previous milestone years. Daniel Mauser’s father, Tom Mauser, decided to set up the vigil after learning school officials did not plan to organize a large community event as they did on the 20th anniversary.

Mauser, speaking at the event, urged the world to “never forget the victims of Columbine,” nor “the injured, the traumatized and their families.”

Nathan Hochhalter, whose sister Anne Marie was paralyzed after she was shot at Columbine, spoke about being trapped in a classroom at the school with about 30 students as they heard gunfire nearby. They were rescued about four hours later by SWAT officers who he said frisked them five times. Six months later, his mother, who had bipolar disorder, took her own life after asking to look at a gun in a pawnshop and shooting herself there.

“I just want to use this moment to let everyone know that it’s OK to ask for help, whatever your situation is whether, either as a survivor 25 years later or someone struggling with any part of their life. These things come in waves and they can hit you when you least expect it. You should all know that we’re all here for you and that you’re not alone,” Hochhalter said.

The victims of Columbine have also been honored at Littleton’s Clement Park, where a memorial was installed in 2007. Personal statements from the families of those lost are inscribed on each, and also available to view online.

In addition to Friday’s vigil, Columbine students, staff and alumni are planning a day of service to honor and remember those killed.

“We invite you to join over 1,000 Columbine students, teachers, families and community members in remembering the lives lost, reflecting on the lives forever changed, and committing to the power of service in your own community,” the organizers write.

The Associated Press contributed to this report.