LITTLETON, Colo. -- Fifteen years after Eric Harris and Dylan Klebold stalked the halls of Columbine High School in a murderous rampage, memories of that fateful day still echo across Colorado and the country.
Schools have tightened security, with more deploying metal detectors or armed guards. Police officers flood into shooting situations, rather than hanging back. School psychologists are trained to intervene more decisively when they encounter students with mental health challenges.
But while the killings that day prompted changes, the school itself continues to shape the minds of kids, none of whom were even there when the tragedy occurred on April 20, 1999.
Armed with guns and bombs, Harris and Klebold killed 12 students and a teacher, Dave Sanders, before committing suicide.
As he has every year since the shooting, Columbine Principal Frank DeAngelis today will read the victims' names in the school to mark the moment everything changed. This will be the last time DeAngelis reads the names as principal. He's retiring in June.
Though he struggled with survivor's guilt, DeAngelis says his priest told him he was spared for a reason.
"If I would've left, I would've struggled," DeAngelis says. "I needed this place ... and they allowed me to fulfill something that needed to fulfilled, and that was to build this community back up."
In the years that followed, DeAngelis has been called upon to aid shooting survivors at Sandy Hook and Virginia Tech, sharing his experience and explaining how both big and little things can re-traumatize victims. At Columbine, administrators changed the fire alarm sound and stopped serving Chinese food in the cafeteria to avoid invoking the smells and sounds of that day.
"I always get asked is when do things get back to normal," DeAngelis says. "Well, you will have to redefine what normal is."
For Coni Sanders, working toward normal after her father Dave's death meant becoming a licensed counselor. She now treats criminals in an effort to help prevent further violence.
"A lot of the victims really wanted to help other victims of tragedies," she says.
Sanders also joined Colorado Ceasefire, which lobbies to strengthen gun-control laws.
The group on Saturday sponsored a remembrance service at the Columbine Memorial. As the sun peeked through gray clouds and occasional raindrops fell, Sanders said she could feel her father's presence even now as she tearfully remembered his death. She then read aloud the names of the 13 victims, her daughter ringing a bell after each.
"We have a purpose. We have repurposed our anger to hope that nobody has to travel this path that we have," Sanders said.
DeAngelis says the past 15 years have given the school and the community time to heal.
"Unfortunately, there will be more school shootings, and I will be there to help," he says. "Maybe, just maybe, hearing my words might just prevent another one."