DENVER (AP) — The 12 students and one teacher killed in the Columbine High School shooting will be remembered Friday in a vigil on the eve of the 25th anniversary of the tragedy.

The gathering, set up by gun safety and other organizations, is the main public event marking the anniversary, which is more subdued than in previous milestone years.

Former Arizona Congresswoman Gabby Giffords, who began campaigning for gun safety after she was nearly killed in a mass shooting, will be among those speaking at the vigil. So will Nathan Hochhalter, whose sister Anne Marie was paralyzed after she was shot at Columbine. Several months after the shooting, their mother, Carla Hochhalter, took her own life.

The organizers of the vigil, which will also honor all those impacted by the shooting, include Colorado Ceasefire, Brady United Against Gun Violence and Colorado Faith Communities United Against Gun Violence, but they say it will not be a political event.

Tom Mauser, whose son Daniel, a sophomore who excelled in math and science, was killed at Columbine, 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, who became a gun safety advocate after the shooting, said he realizes that it takes a lot of volunteers and money to put together that kind of event but he wanted to give people a chance to gather and mark the passage of 25 years since the shooting, a significant number people can relate to.

“For those who do want to reflect on it, it is something for them,” said Mauser, who is on Colorado Ceasefire’s board and asked the group to help organize the event at a church near the state Capitol in Denver. It had been scheduled to be held on the steps of the Capitol but was moved indoors because of expected rain.

Mauser successfully led the campaign to pass a ballot measure requiring background checks for all firearm buyers at gun shows in 2000 after Colorado’s legislature failed to change the law. It was designed to close a loophole that helped a friend of the Columbine gunmen obtain three of the four firearms used in the attack.

A proposal requiring such checks nationally, inspired by Columbine, failed in Congress in 1999 after passing the Senate but dying in the House, said Robert Spitzer, professor emeritus at the State University of New York-Cortland and author of several books on gun politics.

Democratic presidential candidate Al Gore ran on a gun safety agenda against Republican George W. Bush the following year, but after his stance was mistakenly seen as a major reason for his defeat, Democrats largely abandoned the issue for the following decade, Spitzer said. But gun safety became a more prominent political issue again after the 2012 Sandy Hook shooting, he said.

Without much action nationally on guns, Democrat-led and Republican-controlled states have taken divergent approaches to responding to mass shootings.

Those killed at Columbine included Dave Sanders, a teacher who was shot as he shepherded students to safety during the attack. He lay bleeding in a classroom for almost four hours before authorities reached him. The students killed included one who wanted to be a music executive like his father, a senior and captain of the girls’ varsity volleyball team, and a teen who enjoyed driving off-road in his beat-up Chevy pickup.

Sam Cole, another Colorado Ceasefire board member, said he hopes people will come out to remember the victims and not let the memory of them fade. The students killed would now be adults in the prime of their lives with families of their own, he said.

“It’s just sad to think that they are always going to be etched in our mind as teenagers,” he said.