On 20th Anniversary of Columbine, Deaths Still Haunt Principal: 'They Will Always Be My Kids'  

Moments after shots rang out in the hallways of Columbine High school, principal Frank DeAngelis found himself face to face with one of the two teenage gunmen responsible for one the worst school shootings in U.S. history.

“I saw the gunman about 100 yards from me,” DeAngelis tells PEOPLE.

It was 17-year-old shooter Eric Harris.

“I remember shots being fired and glass breaking behind me,” he says. “My worst nightmare became a reality.”

On the morning of April 20, 1999, Harris and fellow student 18-year-old Dylan Klebold shot and killed 12 students and one teacher, as well as wounding 24 others. These actions forever changed DeAngelis, his community in Littleton, Colorado — and the nation.

Now, on the 20th anniversary of the massacre, DeAngelis is opening up for the first time about the events that unfolded that day — and how he and the community struggled in the years that followed in his new memoir, They Call Me ‘Mr. De’: The Story of Columbine’s Heart, Resilience and Recovery.

In the book, he recounts some of the “miracles” that happened that fateful day. Just as shots were ringing out in the hallway where DeAngelis was walking, a group of girls happened to pile out of the locker room on their way to gym class.

“They were right in the crossfire of the gunman,” says DeAngelis, who retired in 2014. “I got them into an area away from the gunman, but he continued to come after us.”

DeAngelis needed to get the terrified girls into the gym, but the doors were locked.

He just had to find the right key — out of 35 on his key ring.

“The first key I pulled out, I stuck it in the door, and it opened,” he says. “On the first try. It’s pretty remarkable.”

He still gets teary-eyed when those students, who are now in their late 30s, send him pictures of their own children.

“They say, ‘If it wasn’t for you, these kids wouldn’t be here and I wouldn’t be here,'” he says.

Not a day goes by when he doesn’t think about the teacher and the 12 students who were killed that day. (He pays tribute to them in a touching memorial at the end of the book.)

“They are my kids, and they’ll always be my kids,” he says. “As a parent, you want to protect your kids at all costs, and on that day, unfortunately, 12 of my kids and one of my dear friends, Dave Sanders, died.”

DeAngelis opens up about the difficulties he faced in the aftermath of the shooting and how therapy helped him cope with the grief and PTSD he endured.

Others didn’t fare as well, including some members of the community who later died by suicide.

DeAngelis was saddened by news of the March 25 suicide of Jeremy Richman, whose daughter died in the 2012 Sandy Hook Elementary School shooting. DeAngelis got to know him when Richman visited Columbine after losing his daughter. “It’s devastating,” DeAngelis says. “Another life gone as a result of tragedy.”

His mission with the book, and with his life in general in the years since the shooting, is to help others. One way he is doing that is by counseling people and working with the Principal Recovery Network to help other school principals dealing with the aftermath of shootings — something he’s been doing for years.

He appreciates the help he got along the way, like the advice his longtime parish priest gave him shortly after the Columbine massacre.

“I started to question my faith,” he says. “Father Ken Leone called me down to the parish and said, ‘Frank, you should’ve died that day. But God’s got a plan for you.’

“He said, ‘Many times, difficulties are really lessons in disguise. God is going to be with you every step of the way.’ I went back to Columbine for 15 more years.”