Since the 1999 massacre, 415 people have been killed in U.S. school shootings.
The epicenter of the Columbine High School mass shooting was the library, where Craig Scott was studying for a biology test on April 20, 1999. Scott, then 16, said he had just sat down next to his friend, Matt Kechter, when his life turned upside down.
This week marks 25 years since two seniors at the Colorado high school committed one of the most infamous school shootings in American history, killing 12 students and a teacher. The shooting left 21 others with gunshot wounds and three with injuries suffered in the ensuing chaos.
Now, at age 41, Scott told ABC News that he still vividly recalls the horror and the carnage he witnessed that day while hiding under a desk in the library "paralyzed with fear" as the two gunmen were just inches away.
"Some people were begging for their life. And (the gunmen) treated it like it was a game and seemingly having fun doing it, and just totally disconnected with the life that they were robbing," Scott said.
RELATED: 25 years after Columbine, steps taken in hospitals to provide gun awareness for children
"They came over to where I was," Scott continued. "They saw my friend, Isaiah (Shoels). At my school, Isaiah was one of the very few African American students. One of them called the other one over and started to call Isaiah racial slurs. They tried to drag him out from under the table. And they shot and killed Isaiah, shot and killed my friend, Matt. They left me under there. I thought I was going to die."
By some miracle, Scott said, he got out safely, covered in the blood of another injured classmate whom he helped escape, only to learn his own sister, 17-year-old Rachel Joy Scott, was the first victim slain in the rampage.
Also killed were Daniel Rohrbough, 15; Kyle Velasquez, 16; Steven Curnow, 14; Cassie Bernall, 17; Lauren Townsend, 18; John Tomlin, 17; Kelly Fleming, 16; Daniel Mauser, 15; Corey DePooter, 17; Dave Sanders, 47; and 16-year-old Kechter and 18-year-old Shoels.
The shooters took their own lives in the library that day, the Jefferson County Sheriff's Office said.
At the time, the massacre in the suburban Denver suburb of Littleton was the deadliest school shooting in U.S. history. There had only been a few of note before it. The 1979 shooting at Grover Cleveland Elementary School in San Diego left two dead and nine wounded; A 1989 shooting at another Cleveland Elementary School in Stockton, California, left 5 dead and 32 wounded. Two were killed and 25 were injured in the 1998 Thurston High School shooting in Springfield, Oregon.
The only other tandem school shooters in U.S. history were a 13-year-old and an 11-year-old who killed four classmates and a teacher in 1998 at Westside Middle School in Jonesboro, Arkansas. The pair were tried and convicted as juveniles and were released from prison when they turned 21.
The Columbine shooting wasn't eclipsed until nearly eight years later when on April 16, 2007, a 23-year-old student fatally shot 32 people at Virginia Tech -- the deadliest school shooting in U.S. history. Like the Columbine shooters, the Virginia Tech shooter died by suicide.
Since the Columbine attack, 415 people have been killed in school shootings as of April 2, 2024, and 907 have been wounded, according to an ABC News review of the Gun Violence Archive, a website that tracks all shootings in the United States. Fifty-five of the attacks were mass shootings, which the Gun Violence Archive defines as four or more people injured or killed, not including the perpetrator.
In 1999, Columbine was among six school shootings in the United States, according to the Gun Violence Archive. In 2024 alone, there have already been 47 shootings at U.S. schools as of April 2, including one on Jan. 4, 2024, that left a student dead and seven people injured, including the principal, at Perry High School in Iowa.
"I truly believe that it was the beginning of the 24/7 news cycle. And it was brought into the living rooms," Frank DeAngelis, who was the principal at Columbine High School at the time of the massacre, said of why that attack has left an indelible mark on the nation.
"And what really haunts me a little bit is thinking that we're still talking about Columbine to the fact that when there is another school shooting ... they make references to 'another Columbine attack,'" the 69-year-old DeAngelis, who retired in 2014 after 35 years as a teacher and school administrator, told ABC News.
But DeAngelis said that while each new school shooting immediately brings him back to the Columbine attack, there have been an incalculable number of lives saved since the mass shooting because of a dramatic shift in training and preparedness.
"Back in 1999 ... the only drills we did at Columbine were fire drills," DeAngelis said.
Named in honor of the retired principal, the Frank DeAngelis Center for Community Safety in Wheat Ridge, Colorado, has provided active-shooter training to more than 170,000 school resource officers, SWAT team members and other law enforcement officers, paramedics and even Navy SEALs, said DeAngelis.
"The police, at that time, had something called 'secure the perimeter' where they had to wait for the SWAT team to get there," DeAngelis said. "So now we're training single officers to go in. And it really is a center that prepares to stop these things from happening."
DeAngelis added, "We are doing some things differently that are saving lives. But we can't give up hope because there are perpetrators out there who are still planning these events. And we just can't accept it as a way of life."
Craig Scott said that on the day of the attack, he made himself and his sister, Rachel, late for school, recounting that "I had to have my hair just perfect."
"We got into this fight," Scott said. "She pulled up and actually dropped me at the front of the school and then went to go park even though I was making us late. I got out and slammed the car door shut on her and walked in the school. I had no idea that that would be the last time I would see her."
He said about a month before his sister was slain, she wrote an essay for a class titled, "My Ethics, My Codes of Life." He said he adopted it as his mantra for life.
"She talked about showing mercy and forgiveness to people who had wronged her," he said. "She said, 'I have this idea that if one person will go out of their way to show compassion, it will start a chain reaction of the same and people will never know how far a little bit of kindness can go.'"
Around the same time his sister was writing the essay, the two shooters -- 18-year-old Eric Harris and 17-year-old Dylan Klebold -- were making videotapes in the basement of one of their homes, talking about starting a revolution and creating a chain reaction, according to investigators. In the aftermath of the attack, Jefferson County officials allowed some of the victims' families and several media outlets to view the video of the killers planning their attack. The Jefferson County Sheriff's Office said it destroyed the tapes in 2011.
For the past 25 years, Scott said he has traveled the country sharing his sister's story. He said he plans to launch a new podcast on Saturday, "Pain into Purpose" to tell inspirational stories.
"The biggest factors of my healing were my family, my faith, but also forgiveness," Scott said. "For a couple years, I used to fantasize about killing the shooters. I used to hate them," Scott said. "As I was beginning to travel and share my sister's story, I was meeting people who had been through far worse than I had been and they weren't these angry, bitter people. They were very free and open. And someone told me once, it was very helpful, that 'forgiveness is like setting a prisoner free and finding out that prisoner is you.'"
He said that after his sister's death, his family was going through her journals and belongings. They found on the back of a chest of drawers, an outline Rachel made of her hands when she was 13.
"In the center of one of the hands, she said, 'These hands belong to Rachel Joy Scott, and will someday touch millions of people's hearts.' She had a deep belief that she would have a positive impact and she has," Scott said. "When I survived, I think I immediately felt this deep sense that God had a purpose for me. Whether people have that belief or not, that belief helped me and it's helped me since to believe that there was a deep reason for why this has happened. And I was able to see through the tragedy to purpose."
Another Columbine survivor, Krista Hanley, told ABC News that she is still coping with the trauma and diagnosed PTSD.
"Every time there's a shooting it brings back the trauma. I think that trauma sticks inside of our bodies. We feel it viscerally," Hanley said.
Hanley said she also has dealt with a lot of survivor's guilt over the last 25 years.
"I even have guilt now that I'm going through life, that I'm able to make decisions to buy a home, to do all these things and my peers, their lives were cut short and they never had those opportunities," Hanley said. "And so there's an incredible amount of guilt that I think comes with surviving. And again, all we can do is live our lives."
She recalled being in the lunch line in the school cafeteria on the day of the attack.
"It was three days after the prom, so I'm sure that prom was on my mind, and I still had my red painted fingernails from prom," Hanley said. "Someone ran through the room ... yelling, 'Get down!' We didn't know about school shootings in 1999. It was not something that I thought of immediately. I thought it was a senior prank. That was something we did in 1999."
She said that at some point, "something shifted in the energy of that cafeteria, and everyone bolted away from the windows that were toward the parking lot and started going up the stairs."
Still on the ground, Hanley said she and some friends scooted around a corner and found themselves in a little hallway she previously didn't know existed.
"We stayed in this hallway a few minutes and then this door opened. To me, it felt like this magic door opened. One of the teachers had opened the door into the auditorium and we went in the auditorium," she said.
From the auditorium, she and other students with her went to the second floor and out a side door.
"We ended up having to climb over a chain link fence, and then we walked through this parking lot that's in the park behind the school," Hanley said. "One person we knew had a cell phone, you know one of those big cell phones. He was graciously letting everyone call people who wanted to call."
Hanley said she called her mother, who was a teacher at a school near Columbine that was on lockdown. But then the phone went dead. She said she eventually walked to a restaurant about a mile away where a parent gave her a ride home.
"I spent the rest of the day glued to the television at home alone, watching things unfold at my school," Hanley said.
In the two-and-a-half decades since the attack, Hanley said she has tried therapy, yoga, acupuncture and massage to help get over her trauma.
After a person she knew became one of 12 people killed in a 2012 mass shooting at a movie theater in Aurora, Colorado, she said she faced "a turning point."
"I felt so helpless to be with my friends, who had lost their best friend. And again to have survived, and then to not be able to do anything or say the right words or address this, that it just is devastating," Hanley said.
She said the experience motivated her to become an advocate and she co-founded the self-defense organization We Are Safer Together.
"It's directly related, of course, to my experience being a survivor of a mass shooting and sort of the subsequent lack of safety that I've felt in my life and in the world," Hanley said. "I took a few self-defense classes in the mid-2000s and they changed my life. Like it really helped my healing process. Learning self-defense, it really helped me feel safer and feel like I could actually ... go through the world with more empowerment."
She said her organization focuses on adaptive self-defense for people with disabilities, marginalized people and those "who may not feel like the self-defense world is actually serving them." She said she is teaching more than just physical self-defense, but also delves into active shooter training, emergency preparedness and emergency planning for businesses and groups.
Hanley said part of her motivation is driven by having "very little hope that things will change."
"Things should have changed after Columbine. Columbine should have been the last shooting in America, the last school shooting. And then especially after Newtown," Hanley said, referring to the 2012 shooting at Sandy Hook Elementary School in Connecticut that killed 26 people, including 20 children. "That hit me so hard, and the fact that we're just continuing to let this happen."
DeAngelis said he has dealt with "a lot of survivor's guilt" and credits years of counseling for helping him cope. He said the teacher who died in the Columbine attack, Dave Sanders, likely saved his life.
The former principal said he was in his office getting ready to offer a student-teacher a full-time contract when his secretary informed him there had been reports of gunfire and pipe bombs in the school.
"As I come out of my office, my worst nightmare becomes a reality because the gunman is coming towards me and I remember it's like he just stopped and the barrel of the shotgun looked about the size of a cannon," DeAngelis said. "I kept thinking what it was going to feel like to have a bullet pierce my body."
Instead of retreating, DeAngelis said he ran toward the killer just as 20 to 25 girls were coming out of a locker room to go to a physical education class.
"I knew if I got the girls into the gymnasium, I would be able to put them in a safe place," he said.
As DeAngelis sprinted toward the killer, Sanders was evacuating students up a staircase and distracted the gunman, who fatally shot him.
At the same time, DeAngelis said he took the moment to try to open the gymnasium but found it locked.
"We hear the sounds of the shots getting louder and he (the gunman) is getting ready to come around the corner," DeAngelis said. "I literally had 30 to 35 keys on a keyring. I reached in my suit pocket. The first key I stick in the door opened it or we wouldn't be having this conversation."
He added, "There's a sign on the highway, and every time I see it, it's the Dave Sanders Memorial, I just point, saying, thank you."
DeAngelis, a devout Catholic, said he believes the only reason he survived the shooting is because "God's got a plan."
He said a few years ago, something happened that "really hit home for me." He was attending a championship game for the Columbine High School softball team, when a woman approached him. He said the woman, now a mother, was one of the girls he let into the gymnasium on the day of the attack.
"She turns me around and said, 'Mr. D, I don't know how to tell you this. I just want to thank you for finding the key because if you didn't, that girl in right field wouldn't be playing in this game because that's my daughter.' And that hit pretty hard," he said.