On April 20, 1999, two seniors at Columbine High School in Littleton High School shot and killed twelve students and one teacher before killing themselves after exchanging gunfire with police. 25 years after the Columbine shooting, school security is a rapidly evolving field in Colorado and elsewhere in the U.S. The Columbine school shooting was the deadliest mass shooting at a U.S. K-12 school in history until it was passed by Sandy Hook in 2012 and Uvalde in 2022.

FILE PHOTO: In an April 20, 1999 file photo unidentified young 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 southwest Denver suburb of Littleton, Colo. (AP Photo/Kevin Higley/file) Kevin Higley/Associated Press

FILE PHOTO: In this April 20, 1999, photo, members of a police SWAT team march to Columbine High School in Jefferson County 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 PHOTO: A woman embraces her daughter after they were reunited following a shooting at Columbine High School in Littleton, Colo., on Tuesday, April, 20, 1999. As many as 25 were killed at the school by two young men who went on a shooting rampage on Tuesday. (AP Photo/Ed Andrieski) Ed Andrieski/Associated Press

Eric Harris, left, and Dylan Klebold are shown during their attack on Columbine High School in a black-and-white still image taken from the security video on April 20, 1999.Courtesy of Wikimedia Commons

Dylan Klebold yells in a video he and Eric Harris made as part of a school project before their 1999 Columbine High shooting rampage. (AP) Associated Press file photo

Columbine gunman Eric Harris is shown firing a pistol in this frame grab of a video tape released by the Jefferson County Sheriff’s Department on Wednesday, Oct. 22, 2003.  AP Photo/Jefferson County Sheriff’s Department

FILE PHOTO: A student from Columbine High School in Littleton, Colo., left, is led away from a home near the school by a relative after the young woman and more than two dozen other students were evacuated from the school on Tuesday, April 20, 1999. Two young men opened fire inside the school and 12 people and a teacher were killed. Two suspects were found dead inside the library hours later, he said. (AP Photo/David Zalubowski) David Zalubowski/Associated Press

FILE PHOTO: A woman stands among 15 crosses posted on a hill above Columbine High School in Littleton in remembrance of the 15 people who died during a school shooting on April 20, 1999. The Associated Press file

FILE PHOTO: A boy looks through the fence at the Columbine High School tennis courts in Littleton, Colo., Saturday, April 24, 1999. Thirteen roses were placed on the fence in remembrance of the 13 people killed by two gun wielding students at the school, Tuesday, April 20, 1999. (AP Photo/Eric Gay)

FILE PHOTO: In this June 9, 2017, photo, members of the Fountain Police Department take part in Active Shooter Response Training exercise at Fountain Middle School in Fountain, Colo. Twenty years after the Columbine High School shooting made practicing for armed intruders as routine as fire drills, many parents have only tepid confidence in the ability of schools to stop a gunman, according to a new poll by The Associated Press-NORC Center for Public Affairs Research.  Dougal Brownlie/The Gazette

In this June 9, 2017, file photo, members of the Fountain Police Department take part in Active Shooter Response Training exercise at Fountain Middle School in Fountain. Twenty years after the Columbine High School shooting made practicing for armed intruders as routine as fire drills, many parents have only tepid confidence in the ability of schools to stop a gunman, according to a new poll by The Associated Press-NORC Center for Public Affairs Research. The Gazette file photo

FILE PHOTO: In this March 27, 2019, photo, Kacey Ruegsegger Johnson poses for a portrait at her home in Cary, N.C. Ruegsegger Johnson, now a mother of four, survived a shotgun blast during the 1999 shootings at Colorado’s Columbine High School that left 12 students, one teacher, and both gunmen dead. The emotional toll of the shooting, joined by fears about their own kids’ safety, spikes each time yet another shooter enters another school. (AP Photo/Allen G. Breed) Allen G. Breed/Associated Press

FILE PHOTO: In this Tuesday, March 12, 2019 photo, former SWAT officer Al Joyce walks in Norway, Maine. Joyce left his job in law enforcement in Jefferson County, Colorado, after a school shooting and now works as a cashier. Joyce was part of the team that in 2006 stormed a classroom in Platte Canyon High School in the town of Bailey, southwest of Denver and saw the aftermath of a shooting. It wasn’t long before the nightmares began and he started drinking heavily to avoid them. He ended up leaving the SWAT team, divorcing his wife and withdrawing from the world. “I wanted to just shut down, turn off,” he said. “It didn’t work out so well.”(AP Photo/Robert F. Bukaty) Robert F. Bukaty/Associated Press

FILE PHOTO: In this Sept. 6, 2016, file photo, students at William Hackett Middle School have their bags checked and pass through metal detectors on the first day of school in Albany, N.Y. Twenty years after the Columbine High School shooting made practicing for armed intruders as routine as fire drills, many parents have only tepid confidence in the ability of schools to stop a gunman, according to a new poll by The Associated Press-NORC Center for Public Affairs Research. (AP Photo/Mike Groll, File) Mike Groll/Associated Press

FILE PHOTO: Retail firearms and gunsmithing shops are ready to temporarily store personal guns for residents who may be suicidal or violent, vacationing or having children over. Jake Tyrrell, owner of JT Tactical Firearms and Gunsmithing, works with a customer at his shop on Thursday, Jan. 30, 2020. Colorado is the first state in the nation to compile an online list of safe storage sites, to help prevent deaths by suicide and create a safe environment for children and adults. (Photo by Jerilee Bennett, The Gazette) JERILEE BENNETT THE GAZETTE

FILE PHOTO: Gene Hill, left, helps Rhonda Grindle bury the end of a cross for Kyle Velasquez, one of the victims killed in the mass shooting at Columbine High School in 1999, just outside the Columbine Memorial on Thursday, April 20, 2023, in Robert F. Clement Park in Littleton, Colo. Grindle went to church with Cassie Bernall, a 17 year old victim of the shooting, and has been putting crosses up near the memorial every year since 1999. (Timothy Hurst/Denver Gazette)Timothy Hurst/Denver Gazette

FILE PHOTO: Will Saggau, a 2001 graduate of Columbine High School who was present during the 1999 mass shooting, pauses and leans over the name of William David Sanders, the teacher killed that day, while visiting the Columbine Memorial on Thursday, April 20, 2023, in Robert F. Clement Park in Littleton, Colo. (Timothy Hurst/Denver Gazette)Timothy Hurst/Denver Gazette

FILE PHOTO: Miles Allison, 4, sits on the east steps of the Colorado State Capitol building among 206 roses, each one representing a victim of school shootings since the 1999 Columbine High School shooting, after he and his family placed the roses on Monday, April 3, 2023 in Denver, Colo. Each rose would eventually have a victim’s name, written on a small card, placed over the rose, though the wind was too harsh to initially place them. (Timothy Hurst/Denver Gazette)Timothy Hurst/Denver Gazette

FILE PHOTO: Deegan Sowder, 6, helps place some of the 206 total roses, each one representing a victim of school shootings since the 1999 Columbine High School shooting, on the east steps of the Colorado State Capitol building with his family on Monday, April 3, 2023 in Denver, Colo. Each rose would eventually have a victim’s name, written on a small card, placed over the rose, though the wind was too harsh to initially place them. (Timothy Hurst/Denver Gazette)Timothy Hurst/Denver Gazette

FILE PHOTO: Will Saggau, a 2001 graduate of Columbine High School who was present during the 1999 mass shooting, places his hand down at the the Columbine Memorial on Thursday, April 20, 2023, in Robert F. Clement Park in Littleton, Colo. (Timothy Hurst/Denver Gazette)Timothy Hurst/Denver Gazette

FILE PHOTO: Freshman Allie Zadrow, center right, hugs classmate Liz Reinhardt at a church after a shooting at nearby Arapahoe High School in Centennial, Colo., on Friday, Dec. 13, 2013. Students from the school were evacuated to the church. Arapahoe County Sheriff Grayson Robinson said the shooter shot two others at the school, before apparently killing himself. (AP Photo/Brennan Linsley) Brennan Linsley/Associated Press

FILE PHOTO: Arapahoe High School students cross the street in front of their school on the first day of classes since a fatal Dec. 13 shooting on campus, in Centennial, Colo., Tuesday Jan. 7, 2014. Students have not attended classes since Karl Pierson, a senior at Arapahoe, entered the school with a shotgun – reportedly with a possible grudge against a teacher – and fatally shot student Claire Davis before killing himself. (AP Photo/Brennan Linsley) Brennan Linsley/Associated Press

FILE PHOTO: Parents stand along the tennis court fence hoping to see if their child is standing outside on the football field after a gunman was spotted inside Arapahoe High School on Friday, Dec. 13, 2013, in Centennial, Colo. Authorities said the gunman shot two students and then turned the gun on himself. The shooting came a day before the anniversary of the Newtown, Conn., attack in which a gunman killed 20 children and six adults at Sandy Hook Elementary School. (AP Photo/The Denver Post, John Leyba) MAGS OUT; TV OUT; INTERNET OUT; NO SALES; NEW YORK POST OUT; NEW YORK DAILY NEWS OUT John Leyba/Associated Press via Denver Post

FILE PHOTO: A parent picks up her daughter at a church where students from nearby Arapahoe High School were evacuated to after a shooting on the Centennial, Colo., campus Friday, Dec. 13, 2013. Arapahoe County Sheriff Grayson Robinson said the shooter shot two others at the school, before apparently killing himself. (AP Photo/Brennan Linsley) Brennan Linsley/Associated Press

FILE PHOTO: Colorado Gov. John Hickenlooper, left, stands with, right to left, state Senate Minority Leader Rep. Bill Cadman, R-Colorado Springs, Colo. House Speaker Rep. Mark Ferrandino, D-Denver, and state Senate President-elect Morgan Carroll, D-Aurora, during a news conference at which they discussed the bipartisan Safe2Tell Act, a measure to fund and run a successful school danger hotline, at the Capitol, in Denver, Tuesday Jan. 7, 2014. Safe2Tell was established after the Columbine high school massacre to give K-12 students an anonymous hotline to report school safety problems to authorities – including planned school shootings, bullying, and planned suicides. (AP Photo/Brennan Linsley) Brennan Linsley/Associated Press

FILE PHOTO: Students are directed to the intersection of East 17th Avenue and City Park Esplanade where parents are waiting for them after a shooting at Denver’s East High School March 22, 2023.Tim Hurst/Denver Gazette

FILE PHOTO: Freshman Treble Brooks hugs his mother Bobbie Brooks after being reunited following a shooting at Denver East High School on Wednesday, March 22, 2023, in Denver.Denver Gazette file

FILE PHOTO: A student, right, hugs a parent as they are reunited following a shooting at East High School, Wednesday, March 22, 2023, in Denver. David Zalubowski/Associated Press

FILE PHOTO: Two women hug after a school shooting at East High School Wednesday, March 22, 2023, in Denver. Two school administrators were shot at the high school Wednesday morning after a handgun was found on a student subjected to daily searches, authorities said. David Zalubowski/Associated Press

FILE PHOTO: Lillie Perez, 11, holds a sign during a “March for Our Lives” protest for gun legislation and school safety March 24, 2018, in Houston. Students and activists across the country planned events Saturday in conjunction with a Washington march spearheaded by teens from Marjory Stoneman Douglas High School in Parkland, Fla., where over a dozen people were killed in February. There have been dozens of shootings and other attacks in U.S. schools and colleges over the years, but until the massacre at Colorado’s Columbine High School in 1999, the number of dead tended to be in the single digits. (AP Photo/David J. Phillip, File) David J. Phillip/Associated Press

FILE PHOTO: For a second straight day, hundreds of Denver East High students descended on the Colorado Capitol Friday in an effort to persuade lawmakers to take action on gun reform bills following another student-involved shooting. Tom Hellauer/Denver Gazette

FILE PHOTO: Students and parents talk with Rep. Eliza Hamrick in the halls outside the House of Representatives during a student protest in response to yesterday’s shooting at Denver East High School, on Thursday, March 23, 2023, at the Colorado State Capitol in Denver Colo. (Timothy Hurst/Denver Gazette) Timothy Hurst/Denver Gazette

FILE PHOTO: From left, Jada Rouse, Sofie Davidson and Drew Moore, hold signs as they listen to speakers outside of the Colorado Capitol on Friday. For a second straight day, hundreds of Denver East High students descended on the Capitol in an effort to persuade lawmakers to take action on gun reform bills following another student-involved shooting.  Tom Hellauer/Denver Gazette

FILE PHOTO: East High School sophomore Anna Hay, 15, talks with Rep. Serena Gonzales-Gutierrez outside of the House of Representatives during a student protest in response to yesterday’s shooting at Denver East High School, on Thursday, March 23, 2023, at the Colorado State Capitol in Denver Colo. (Timothy Hurst/Denver Gazette) Timothy Hurst/Denver Gazette

FILE PHOTO: The “Respect Life” Columbine Colorado license plate in honor of the victims of the school shooting. Courtesy, Colorado Department of Motor Vehicles

FILE PHOTO: Richard Diaz, center, escorts Noel Montoya, left, Serenity Diaz, center and Anna Montoya, right, out of Columbine Elementary after the school was placed under a brief lockdown following an area shooting report in Denver on Wednesday, Feb. 21, 2024. Tom Hellauer/Denver Gazette

FILE PHOTO: A police officer escorts a Columbine Elementary student to their family following a shots fired report near the school leading to a lockdown in Denver on Wednesday, Feb. 21, 2024.Tom Hellauer/Denver Gazette

FILE PHOTO: Militarized Denver Police officers respond to a report of shots fired in the area of Columbine Elementary on Wednesday, Feb. 21, 2024.Tom Hellauer/Denver Gazette