AP PHOTOS: Teen gunmen unleashed terror, chaos at Columbine

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 Li

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 Li

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

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

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 f

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 f

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 respe

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 respe

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

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

FILE - This April 21, 1999, file photo, shows the news media compound near Columbine High School in Littleton, Colo. Twelve students and one teacher w

FILE - This April 21, 1999, file photo, shows the news media compound near Columbine High School in Littleton, Colo. Twelve students and one teacher w

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 Co

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 Co

FILE - In this April 24, 1999, file photo, the casket bearing Columbine High School shooting victim Rachel Joy Scott is signed with notes of remembran

FILE - In this April 24, 1999, file photo, the casket bearing Columbine High School shooting victim Rachel Joy Scott is signed with notes of remembran

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 L

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 L

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

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

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 to

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 to

FILE - In this April 20, 1999, file photo, Fran Allison, right, comforts her daughter Brooke after they were reunited after a shooting at Columbine Hi

FILE - In this April 20, 1999, file photo, Fran Allison, right, comforts her daughter Brooke after they were reunited after a shooting at Columbine Hi

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 o

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 o

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

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

FILE - In this April 20, 1999, file photo, SWAT members run down Pierce Street while a Jefferson County, Colo., Sheriff's Department deputy peers thro

FILE - In this April 20, 1999, file photo, SWAT members run down Pierce Street while a Jefferson County, Colo., Sheriff's Department deputy peers thro

LITTLETON, Colo. (AP) — On April 20, 1999, two teenage gunmen dressed in black trench coats went on a killing 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 United States' deadliest 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.