Columbine Shootings 10 Years Later: Students, Teacher Still Haunted by Post-Traumatic Stress

First in a series on the Columbine shootings, 10 years later.

On April 20, 1999, Columbine High School seniors Eric Harris and Dylan Klebold slaughtered 12 and...

On April 20, 1999, Columbine High School seniors Eric Harris and Dylan Klebold slaughtered 12 and injured 24 in a 45-minute shooting rampage. Though the Columbine shooting rampage is a decade old, psychological wounds are still raw, according to, from top, Mark Taylor, Kent Friesen and Anne Marie Hochhalter.

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At his worst after he survived the Columbine shootings in Littleton, Colo., chemistry teacher Kent Friesen would become physically ill, often throwing up. Now, a decade later, certain triggers can still set off crying jags.

Friesen remembers running past the bodies of two students in the science wing that day as he tried to get help for girls' basketball coach Dave Sanders, who was gunned down and eventually bled to death in the melee.

"I knew he was going to die," said Friesen, who has had to unearth the trauma again as the victims, the country -- and the media -- brace for the 10th anniversary of the most iconic of all school shootings.

On April 20, 1999, Columbine High School seniors Eric Harris and Dylan Klebold, wielding automatic weapons, slaughtered 12 students and one teacher. Another 24 were injured in the 45-minute rampage.

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Though Columbine is now a decade old -- and a larger shooting at Virginia Tech that left 32 dead followed in 2007 -- the wounds of this tragedy are still raw.

A number of books have tried to dissect the motives of the killers and the truth behind the event that played out on television screens across America, but no studies have ever examined the psychological effects of the massacre on those left behind, according to Dr. Frank Ochberg, a former FBI psychiatrist who guided the counseling teams in the aftermath of Columbine.

"There were relatively few who were right at the heart of [the shootings] and were direct post-traumatic stress syndrome candidates," Ochberg told ABCNews.com. "But there were relatively many for whom Columbine was their Gettysburg."

"It changed them, and if they were young, they grew up fast," he said. "Within that group, some are better and some are worse."

Friesen had been holed down in his classroom for three hours that day, with the incessant blaring of the school alarms, exploding pipe bombs and students' screams.

"A gun and holster is the worst one for me," said the 58-year-old, who has retired from teaching and lives in Littleton. "But you live with it. You learn to cope."