School shooting

In photos: Colorado marks Columbine High School massacre, 20 years on

 Columbine High School Shooting survivors Sean Graves, left, hugs Patrick Ireland during the Columbine: 20 memorial night.
Columbine High School Shooting survivors Sean Graves and Patrick Ireland. Photo: Hyoung Chang/MediaNews Group/The Denver Post via Getty Images

Community members, survivors and victims' families came together at Clement Park in Littleton, Colorado, to mark 20 years since the Columbine High School shooting massacre.

Details: A series of events honored those affected by the shooting, which killed 12 students and 1 teacher on April 20, 1999, including a remembrance ceremony. At the event, audience members cried and cheered survivor Sean Graves' onto the stage, the Denver Post reports. Here are some of the most powerful moments from the events.

 Michael Scott (R) and Marie Sophie (L) visit the grave of his sister, Rachel Scott, at the Chapel Hill Memorial Gardens in Littleton, Colorado.
Michael Scott (R) and Marie Sophie (L) visit the grave of his sister, Rachel Scott, at the Chapel Hill Memorial Gardens in Littleton, Colorado. Photo: Jason Connolly/AFP/Getty Images
The Queen City Pipe Band marches past the crowd at the end of the Columbine Remembrance Ceremony.
The Queen City Pipe Band marches past the crowd at the end of the Columbine Remembrance Ceremony. Photo: Jason Connolly/AFP/Getty Images
 Michelle Aguayo of Morrison, Colorado and her daughter, Ciara Shannon, of Boulder, Colorado, stop by an ad hoc display of crosses with the names of students killed in the 1999 attack.
Michelle Aguayo and her daughter, Ciara Shannon, view crosses with the names of students killed in the 1999 attack. Photo: Joe Mahoney/Getty Images
 Michael Scott (R) and Marie Sophie (L) visit the grave of his sister, Rachel Scott, at the Chapel Hill Memorial Gardens in Littleton, Colorado.
Michael Scott (R) and Marie Sophie (L) visit the grave of his sister, Rachel Scott, at the Chapel Hill Memorial Gardens in Littleton, Colorado. Photo: Jason Connolly/AFP/Getty Images
 Columbine High School teacher Ivory Moore (C) rallies up community members during the Columbine Remembrance Ceremony.
Columbine High School teacher Ivory Moore (C) rallies up community members during the remembrance ceremony. Photo: Jason Connolly/AFP/Getty Images
A video message from President Bill Clinton  is played on a screen during the Columbine Remembrance Ceremony.
A video message from President Bill Clinton is played on a screen during the remembrance ceremony. Photo: Jason Connolly/AFP/Getty Images
Columbine High School students gather with community members at the remembrance service.
Columbine High School students gather with community members at the remembrance service. Photo: Jason Connolly/AFP/Getty Images
Flowers are placed at the "Columbine: 20 years" event  in honor of those impacted by the massacre.
Flowers are placed at the "Columbine: 20 years" event in honor of those impacted by the massacre. Photo by Hyoung Chang/MediaNews Group/The Denver Post via Getty Images
Flowers bloom at the Columbine Memorial in Clement Park.
The Columbine Memorial in Clement Park. Photo: Hyoung Chang/MediaNews Group/The Denver Post via Getty Images
Candles wrap around a collection of flowers at the Columbine Memorial at Clement Park in Littleton, Colorado, during a community vigil.
A community vigil for the Columbine High School shooting victims. Photo: Jason Connolly/AFP/Getty Images

Three decades of school shootings

Quote on a wall from a student about school shootings
Kailey Slusher casts a shadow yesterday on the Columbine Memorial in Littleton, Colo. Photo: Joe Mahoney/Getty Images

Today marks the 20th anniversary of the attack on Columbine High School: On April 20, 1999, 2 teenage boys dressed in black trench coats killed 12 classmates and a teacher, and wounded 2 dozen others before taking their own lives.

Why it matters: Now, the survivors are raising kids in a world shaped by the attack. "Drills teaching students to 'lock down' inside classrooms became routine. Schools formed teams to assess threats, particularly from students. And security firms forged a multibillion-dollar industry, introducing surveillance video, panic buttons and upgraded doors and locks," AP reports. And, sadly, mass shootings have become part of growing up in America.