AP PHOTOS: Teen gunmen unleashed horror at Columbine in 1999

FILE - In this April 20, 1999, file photo, members of a police SWAT team march to Columbine High School in Littleton, Colo., as they prepare to do a final search of the school after two gunmen opened fire on campus. The shooting shocked the country as it played out on TV news shows from coast to coast. (AP Photo/Ed Andrieski, File)
FILE - In this April 24, 1999, file photo, students embrace each other at a makeshift memorial for their slain classmates at Columbine High School on a hilltop overlooking the school in Littleton, Colo. Twelve students and one teacher were killed in a murderous rampage at the school on April 20, 1999, by two students who killed themselves in the aftermath. (AP Photo/Bebeto Matthews, File)
FILE - In this April 25, 1999, file photo, a young girl holds a rose as she is held during a prayer at a memorial service on for the victims of the Columbine High School shooting rampage in Littleton, Colo. Twelve students and one teacher were killed in a murderous rampage at the school on April 20, 1999, by two students who killed themselves in the aftermath. (AP Photo/Eric Gay, File)
FILE - In this April 20, 1999, file photo, Fran Allison, right, comforts her daughter Brooke after they were reunited after a shooting at Columbine High School in Denver. Twelve students and one teacher were killed in a murderous rampage at the school on Tuesday, April 20, 1999, by two students who killed themselves in the aftermath. (AP Photo/Ed Andrieski, File)
FILE - In this April 20, 1999, file photo, women head to a library near Columbine High School where students and faculty members were evacuated after two gunmen went on a shooting rampage in the school in the Denver suburb of Littleton, Colo. Twelve students and one teacher were killed in a murderous rampage at the school on April 20, 1999, by two students who killed themselves in the aftermath. (AP Photo/Kevin Higley, File)
FILE - In this April, 20, 1999, file photo, a woman embraces her daughter after they were reunited following a shooting at Columbine High School in Littleton, Colo. The shooting shocked the country as it played out on TV news shows from coast to coast. Images from the scene showed terrified students fleeing the school, SWAT officers waiting to enter and an injured boy trying to escape through a window. (AP Photo/Ed Andrieski, File)
FILE - In this April 21, 1999, file photo, from left, Rachel Ruth, Rhianna Cheek and Mandi Annibel, all 16-year-old sophomores at Heritage High School in Littleton, Colo., console each other during a vigil service to honor the victims of the shooting spree in Columbine High School in the southwest Denver suburb of Littleton, Colo. Twelve students and one teacher were killed in a murderous rampage at the school on April 20, 1999, by two students who killed themselves in the aftermath. (AP Photo/Laura Rauch, File)
FILE - In this April 28, 1999, file photo, a woman looks at crosses posted on a hill above Columbine High School in Littleton, Colo., in remembrance of the people who died during a shooting rampage at the school. Twelve students and one teacher were killed in a murderous rampage at the school on April 20, 1999, by two students who killed themselves in the aftermath. (AP Photo/Eric Gay, File)
FILE - In this April 20, 1999, file photo, students from Columbine High School are led away from the facility after two gunmen went on a shooting rampage, in the southwest Denver suburb of Littleton, Colo. Twelve students and one teacher were killed in a murderous rampage at the school on April 20, 1999, by two students who killed themselves in the aftermath. (AP Photo/David Zalubowski, File)
FILE - In this April 22, 1999, file photo, Columbine High School students, from left, Darcy Craig, Molly Byrne and Emily Dubin stop to pay their respects at a makeshift memorial set up in a park near the high school in Littleton, Colo. On April 20, 1999, two teenage gunmen went on a killing rampage at Columbine High School in suburban Denver. (AP Photo/Eric Gay, File)
FILE - This April 21, 1999, file photo, shows the news media compound near Columbine High School in Littleton, Colo. Twelve students and one teacher were killed in a murderous rampage at the school on April 20, 1999, by two students who killed themselves in the aftermath. (AP Photo/Ed Andrieski, File)
FILE - In this June 15, 1999, file photo, tape marks the line in front of the doors to the library in Columbine High School as members of the media took their first trip through the school in the southwest Denver suburb of Littleton, Colo. Twelve students and one teacher were killed in a murderous rampage at the school on April 20, 1999, by two students who killed themselves in the aftermath. (AP Photo/David Zalubowski, File)
FILE - In this April 20, 1999, file photo, SWAT members run down Pierce Street while a Jefferson County, Colo., Sheriff's Department deputy peers through a fence to keep an eye on Columbine High School after a pair of gunmen went on a shooting rampage inside the facility in Littleton, Colo. (AP Photo/David Zalubowski, File)
FILE - In this April 27, 1999, file photo, Krista Sleeth, Bev Fleer and Cindy Sleeth embrace while standing on a hill above Columbine High School in Littleton, Colo., during a moment of silence for the victims. Twelve students and one teacher were killed in a murderous rampage at the school on April 20, 1999, by two students who killed themselves in the aftermath. (AP Photo/Michael S. Green, File)
FILE - In this April 24, 1999, file photo, a boy looks through the fence at the Columbine High School tennis courts in Littleton, Colo. Thirteen roses were placed on the fence in remembrance of the 13 people killed by two gun wielding students at the school. (AP Photo/Eric Gay, File)
FILE - In this April 24, 1999, file photo, the casket bearing Columbine High School shooting victim Rachel Joy Scott is signed with notes of remembrance from family members as it sits at the Trinity Christian Center in Littleton, Colo. Twelve students and one teacher were killed in a murderous rampage at the school on April 20, 1999, by two students who killed themselves in the aftermath. (AP Photo/Rick Wilking, Pool, File)

LITTLETON, Colo. — On April 20, 1999, two teenage gunmen dressed in black trench coats went on a rampage at Columbine High School in suburban Denver.

They shot and killed 12 classmates and a teacher and wounded two dozen others in what was then the deadliest U.S. school shooting. The boys then took their own lives.

The shooting shocked the country as it played out on TV news shows from coast to coast. Images from the scene showed terrified students fleeing the school , SWAT officers waiting to enter and an injured boy trying to escape through a window.

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