DENVER - The deadly shooting at an elementary school in Newtown, Connecticut on Friday is bringing back memories of that terrible day in 1999 when two young gunmen opened fire at a school near Littleton, Colorado.
Frank DeAngelis was the principal at Columbine during the massacre in 1999 and remains the principal there today.
"We're here to provide all the support they need and the message I would like to send to them is 'they're not in this alone,'" DeAngelis said Friday, a few hours after the shooting in Connecticut.
DeAngelis said he received a call Friday from a reporter in New York who asked when things would return to normal for the families affected by the killings.
"I said very politely, 'It will never get back to normal.' What happened today, just like what happened at Columbine High School, what happened up at Platte Canyon High School, what happened at Virginia Tech, what happened at Chardon [High School] last Feburary - you have to redefine what normal is."
It was a Tuesday morning in April of 1999 when reports began to come in about a gunman on the football field at Columbine High School.
We soon learned that the gunmen were students at the school -- two seniors and friends -- Eric Harris, 18, and Dylan Klebold, 17.
The teenagers came into the school and set up pipe bombs in the cafeteria, then started shooting fellow students in the library and the nearby area.
The bombs didn't go off. Harris and Klebold committed suicide, but not before taking the lives of 12 students and one teacher.
Although the situation at Columbine was admittedly different from what happened Friday in Newtown, DeAngelis said all the mass shootings in the United States begs a question about when the nation will take action.
"I think as a society we have to come together and have to stop these senseless deaths," DeAngelis said. "We have to stand up as a nation and say, 'Enough is enough. What is wrong with our society?'"
Lives lost at Columbine High School:
Thirteen lives were lost at Columbine High School -- remembered not only by friends and family, but a grieving community that built a memorial at the park near the school.
Cassie Bernall. A born-again Christian who was active in church youth programs and Bible study groups.
Steven Curnow. A Star Wars fan who dreamed of being a Navy Top Gun and piloting an F-16.
Corey Depooter. He loved to golf, hunt and fish. He had recently taken a job at a golf club to save up for a boat with a friend.
Kelly Fleming. She was an aspiring songwriter and author.
Matthew Kechter. He hoped to start for the Rebels' football team.
Daniel Mauser. He earned straight A's on his last report card. He ran cross-country and joined the debate team.
Daniel Rohrbough. He helped in his father's electronics business and worked on family farms during the summer. He was shot holding an exit door open for fleeing students.
William "Dave" Saunders. A teacher at Columbine for 24 years. He coached girls' basketball and softball.
Rachel Scott. She had recently played the lead in a student play.
Isaiah Shoels. He wanted to attend arts college and become a music executive.
John Tomlin. He went on a missionary trip to Mexico with his family and built a home for the underprivileged.
Lauren Townsend. She was captain of the varsity volleyball team. She wanted to major in biology in college.
Kyle Velasquez. Neighbors said his personality touched everyone he met.
Lessons learned from Columbine:
At the 10th anniversary ceremony for the Columbine victims, a father from Richmond, Va. said that new police tactics that emerged after Columbine probably saved his son's life. Andrew Goddard's son Colin was wounded at the Virginia Tech University massacre in 2007.
"They (Columbine victims) paid a huge price for that small lesson, but that lesson did benefit the students at Virginia Tech," Goddard said.
At Columbine, police and deputies followed a standard tactic of establishing a perimeter before advancing carefully toward the gunmen.
After the lessons learned from Columbine, many agencies adopted a new policy of aggressively attacking a shooter, known as the "active shooter scenario."
Connecticut State Police said that was the tactic they used when they heard about the shooting inside an elementary school in Newtown Friday morning.
"Newtown police immediately upon arrival went into the school," said Connecticut State Police Lt. Paul Vance. "Every crack, every crevice, every portion of that school" was searched.
Virginia Tech student Seung Hui-Cho killed 32 people and committed suicide on April 16, 2007.