Frank DeAngelis started working at Columbine High School in Littleton, Colorado, in 1979. He taught social studies and coached football and basketball, later becoming principal. On the morning of April 20, 1999, DeAngelis was about to begin a meeting in his office when his secretary came to the door, saying there had been a report of gunfire.

DeAngelis ran out into the hallway and into the chaos that would become the most notorious school shooting of the modern era. In less than an hour, two seniors killed 12 students and a teacher, wounded 21 others, and then killed themselves. Before then, the most violent incidents he’d witnessed were a handful of fistfights. Afterward, DeAngelis suddenly found himself at the center of a community wracked with grief.

DeAngelis, who retired from Columbine in 2014, is now heading up a national support network for other principals who’ve experienced shootings at their own schools. He spoke with The Trace about how he led Columbine after the shooting, and how he helps others find their footing after acts of violence at school.

What was going on for you in the hours and days immediately after the shooting?

There was just this weight, this survivor’s guilt. I should have lost my life. That day, I came out of my office and I encountered one of the gunmen. Everything was magnified: the size of his gun, the shots being fired, the alarms going off. I saw some girls coming out of a locker room and they were unaware of the danger. They were my kids, and I needed to protect them. But Dave Sanders, who was a dear friend of mine, he ran up to warn kids, and as he was running down the hallway, the gunman caught a glimpse of him. He turned away from me and shot Dave. He died from his wounds.

That evening, I was at the local elementary school where parents were coming to claim their children. Some of the parents were told that they had to fill out missing persons reports, which meant there was a good chance their kids had died. Seeing their faces was harrowing.

I was really struggling, even with my faith. A couple days later, a priest called and asked me to come down to the church. I said, “Father, I am overwhelmed, I have no time, I’m not in a good place.” He insisted, and when I got there, he leaned over and quoted Proverbs: “A man’s heart plans his way, but the Lord directs his steps.” He told me I was spared for a reason, and I needed to go rebuild that community. At that I felt this inner peace. I decided we’d take it day by day.

Some Columbine teachers left after the shooting. You chose to stay for another 15 years.

The day after the tragedy I addressed the community — faculty, parents, local leaders — and told the kids who were freshmen, “I’m going to be with you until you graduate.” But after three years I still didn’t feel that I had fulfilled what the priest had asked me to do. The job to rebuild the community was not done. So I made a commitment to remain as principal until every kid who was in an elementary school in the Columbine area graduated. I wanted to be their principal; hand out the diploma. And eventually I just made it an even 15.

Everybody tried telling me, “Frank, you need to get away, you’re never going to heal.” But if I had left the school, I would have been worrying about how the recovery process was going for the kids. It’s something I had to do. Columbine was like a second family to me.

Often after these shootings, there’s a public outcry to replace the administration. There were some detractors towards me, because this event happened on my watch. They felt like everything that went wrong was my responsibility. But I had the support of the school board president and others. If Columbine happened today, and I had to deal with the social media and the politics on a daily basis, I don’t know if I would’ve stayed.

A traumatic event can affect people in dramatically different ways. What were some of the responses among teachers and students after the shooting?

Trying to meet the needs of everyone was very difficult. We had students who felt they had to get away, and some parents who did not want their kids to return. We had staff members who, when they walked into the school building, felt a lot of stress. Some of them had to leave, and I understood that.

The students who did return, some felt that they needed to talk about it. So we brought in additional counselors and resources. We trained our teachers to look out for kids that were struggling. And then we had others who did not want to listen to anyone else, who said I don’t need counseling, the sooner I get back to doing what I was doing prior, that’s going to help me heal.

I really stressed that we can agree to disagree, but the most important thing is that we do everything we can to help each other. It was a monumental task.

How did you respond to those newfound needs and sensitivities?

Before the shooting, I didn’t know anything about post-traumatic stress disorder or triggers. I had a great team of psychologists and people from the school district who explained what I needed to be aware of.

For example, we had to make changes to the physical makeup of the building. We got rid of the carpet, because that day a lot of kids had seen blood-stained carpet, and put tile floors in. We repainted the hallways with tranquil colors. We got a fish tank because it was supposed to help the kids relax. Our mascot is the Columbine Rebel, and we had a mural in our gymnasium of a revolutionary rebel with a musket. We put a flag in his hand instead.

Kids could not wear camouflage clothing because many of the police officers that day were wearing camouflage. We couldn’t serve Chinese food because that was a meal they were eating when the shooting started.

The summer after the shooting, a company came in and brought the sounds of different fire systems. I had to sit in a room and listen to all the different alarms, so I could pick one that was distinct from the alarm on the day of the tragedy. I chose one that reminded me of a British siren.

Parents really wanted a lot of security, and we had extra security at school, but the students at times would come up to me and say, “Mr. De, this is no longer like a school, it’s like a fortress.” So we had to find that fine line.

What was the single biggest change you made at the school?

Thirteen people were killed that day. Ten were were killed in the library. We felt pretty strongly that to pay honor to the students who lost their lives, we could not go back into that library. People suggested changing the colors, changing where the doors were, or putting drywall in front of the entrance. But I was concerned if we put drywall there, it would turn into a memorial wall, and I really felt it would retraumatize the kids and the teachers on a daily basis.

We ended up putting lockers in front of where the doors had been. Then we had the floor of the library cut up, and an atrium built above the cafeteria, which is one floor below. Now when you come into the cafeteria, you look up and see a huge mural of aspen trees reaching up to the sky and 13 clouds that represent the 13 people.

You recently helped start a recovery support network made up of principals from other schools that have experienced shootings. What kinds of things do you talk about?

The National Association of Secondary School Principals asked me to head it up. This month we met in person for the first time, 16 other principals and myself. The principal from Stoneman Douglas High School was there, the principal of Marshall County High School, the principal from Great Mills High School.

People have questions like, “What do we do for prom? What do we do for graduation?” A lot of them ask, “Does it get better?” I told them it does get better, don’t give up hope. It’s a marathon, not a sprint.

There are going to be times when you think you’re moving ahead, and then an event happens and it puts the community back in this feeling of despair — like with the recent suicides in Parkland and Newtown. We had two suicides after Columbine, the mother of one of our students who was critically injured, and a student who was in the classroom with Dave Sanders.

Do you think Columbine has healed from what happened?

Our school motto is “We are Columbine.” That rang out so loudly after the tragedy, and brought people together. Unfortunately, Columbine has this legacy, when new shootings happen it’s often mentioned. If you had asked me 20 years ago if we would still be talking about Columbine, I’d say no way.

But we also represent hope and endurance. As the parents and I have been preparing for the 20th anniversary, we decided to focus on all the good that has come out of the tragedy: the scholarships, the new library, the run for remembrance, the student programs, the Rebels Project. Even though I’m not principal anymore, I am still helping the school recover. I will continue doing this until I can no longer walk or talk.