He was principal at Columbine 23 years ago. He gets asked over and over why little has changed.

Frank DeAngelis, or "Mr. De," as his students called him, had been principal of Columbine High School in Littleton, Colorado, for three years on April 20, 1999. At 11:19 a.m. that day, two seniors came to school armed with semiautomatic rifles, pistols and explosives. They killed 13 people and wounded 21 more.

It wasn't the first school shooting in America, and it certainly hasn't been the last.

In 1999, I was a sophomore at Golden High School, a 20-minute drive from Columbine. I had friends who went to school there, and that day marked me for the rest of my life. At the time, I remember thinking something was bound to change after such a horrific school shooting.

But it hasn't. It's gotten worse.

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Since the Columbine shooting, more than 311,000 children have been exposed to gun violence at 331 schools, according to The Washington Post. The attacks have killed at least 185 children, educators and others, and injured 369 people.

Already this year, there have been 27 school shootings, including seven involving fatalities, according to Education Week.

DeAngelis, who retired from Columbine in 2014, is often asked to work with communities and members of the news media after school shootings. His expertise is once again in demand after the mass killing at Robb Elementary School in Uvalde, Texas, where an 18-year-old fatally shot 19 kids and two teachers on May 24.

DeAngelis sat down with members of the USA TODAY Editorial Board to talk about that horrible day in 1999 and what the nation has learned, or failed to learn, about school shootings since 1999.

These questions and answers have been edited for length and clarity:

You were the principal at Columbine on that horrible day. Could you tell me about what you remember from when the shooting started?

DeAngelis: My secretary came running towards me and face-planted and I knew something was wrong. She said there had been a report of gunfire down in the cafeteria, bombs exploding. And this isn't registering me with me because my first instinct is this has to be a senior prank. In my years at Columbine, I can count on two hands the number of fistfights we had, so this was the last place I thought it would happen.

As I came out of my office, I encountered the gunman. And I thought I walked up very calmly. But my secretary said I just sprinted towards the gunman. And all I kept thinking about is what it was going to feel like to be shot.

Be very mad about this: Schoolchildren begged for help with officers waiting outside

I had some of my girl students coming out of the locker room to go to a physical education class. The only drills we did then were fire drills. But I also was familiar with the building and knew if I was able to get the girls into the gymnasium then we'd be able to close the doors, and then finally there was egress to the outside. While everything was going to plan, the gunfire was getting closer, I'm trying to keep the girls calm.

Then I go to pull on a gymnasium door and it's locked. So the girls start screaming, there were girls praying, and all of a sudden the gunman is coming around the corner. I mean the sounds of the shots are just echoing through the halls.

I had a suit on, I reached in my pocket, had about 25 keys on a key ring. The first key I pulled out I stuck in the door and it opened on the first try.

We've learned nothing since Columbine: Texas schoolchildren begged for help with officers waiting outside. Be mad about that.

I got the girls inside and put them in an area where the gymnastic equipment was stored. And I said, "I promise I will be back in to get you but I need to make sure it is safe." And so I go stick my head outside, all the police are arriving. And I said, I need to go get my girls. And they covered me while I went in and got the girls outside.

When does this end? What has to happen for this to end?

DeAngelis: It is so devastating because they continue to happen. But one of the things we can't lose sight of, even though it's difficult talking about this today because of everything that happened at Robb Elementary – there were so many lessons to be learned from Columbine. You know, the key one is first responders because we actually had a school resource officer that was exchanging gunfire, but officers waited 47 minutes before entering the high school. And that was about 58 minutes after the first shots were fired.

Well, now look at what is happening. You have school resource officers, single officers that are engaging immediately.

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I think everyone feels there's going to be one thing that's going to stop this, and I don't agree with that. I think it's a jigsaw puzzle. In the first place, people go to guns. And I understand. I had a legislator from Florida say, "Frank, I can guarantee you 100% that we have tougher gun laws, and there will never be another school shooting." And I said, "I have to disagree."

I think we do need to look at gun legislation. Why do people need automatic weapons for self-defense? But that's not the only thing. The killers at Columbine purchased guns through a gun show. There was a loophole where they didn't do a background check. And she (the purchaser of the guns) came out and said if they would have asked more questions, (she) would have walked out of there.

Those killers purchased three guns from someone they worked with. And how do you stop that? As I said, in addition to looking at legislation that tightens gun laws, we have to look at some of the other things.

I'm concerned when I hear school districts are eliminating social workers or psychologists. Something else is the role social media is playing. Just reading some of the information that came out of Texas: This kid, this killer, was posting things, just like in Parkland.

A lot of these kids are being raised by grandparents, even great-grandparents, and I'm a grandparent, and we're loving, caring. But the last time I raised kids was about 25 years ago.

We need to come together. And I think that's the most important thing.

There's been talk of arming teachers. Would having access to a firearm have helped you at Columbine?

DeAngelis: I could go through gun training classes; I could be adept at firing a weapon. But one of the things that I'm not sure I could have done that day is change that teacher mindset. If I would have been armed, coming out of my office, and all of a sudden I'm running down the hall, and I see this gunman coming towards me, I don't look at him as a killer. I look at him as one of my students.

As educators, we feel we can help every kid no matter what they're going through. And I would have tried to reason with him saying, "What are you doing? There's got to be a better way. Put down the gun." Well, if I would not have been able to talk him down, all of a sudden he shoots me, and then I endanger those other 20 girls that were with me because I did not stop him.

It's easy for people to say, "Yeah, give me a gun." But could you shoot one of the kids that was a student in your class? I don't think I could have done that because I would have tried to reason with them, instead.

Are you still in touch with any students from Columbine?

DeAngelis: Yeah, they're always my kids. You know, one of the things that makes it so difficult is every year on April 20, I call the families that lost their kids. And I've done that for the past 23 years. This past year, I was talking to a father and he said, "You know, my son's birthday," and I said, "Yeah, it was March 2." And he said, "You know, my son would have been 41 years old this year." And it just made me think, oh my gosh, so much of their life was lost on that day.

Carli Pierson, a New York licensed attorney, is an opinion writer with USA TODAY, and a member of the USA TODAY Editorial Board. Follow her on Twitter: @CarliPiersonEsq

You can read diverse opinions from our Board of Contributors and other writers on the Opinion front page, on Twitter @usatodayopinion and in our daily Opinion newsletter. To respond to a column, submit a comment to letters@usatoday.com.

This article originally appeared on USA TODAY: Columbine principal: no single solution to school shootings