Transcript for Somber anniversary of massacre at Columbine High School
We have a sad anniversary to mark this morning, 20 years since columbine. Overnight a vigil, family members, survivors and first responders honoring the 12 students and one teacher killed in that massacre. Clayton Sandell is in Littleton, Colorado with a look at how the country has changed with a shooting that was really a dark milestone in American history. Clayton, good morning to you. Reporter: Good morning to you, Dan. It is hard to believe it's been 20 years since the columbine attack. It was not the first school shooting but many here were hoping it would be the last. Today the community is gathering to honor the lives taken too soon and focus on the work they say still needs to be done. At a vigil here overnight they came to remember 13 names, 12 students and one teacher murdered 20 years ago today. Fellow or former students it's believed who rushed the school and opened fire. Reporter: Two fellow students planned and executed the horrific attack at columbine high school, ushering in the modern era of deadly school shootings. Tom Mauser still wears the shoes his son was wearing the day he was killed. I try not to think about what he would be doing. To me he's still 15. Reporter: Columbine became a rallying cry for copycats, according to an ABC news investigation, believed to have inspired more than 50 attacks, plots or threats since. We're not a tourist attraction and we're not a place for you to come and gain inspiration. Reporter: Just this week the FBI says the 18-year-old Florida woman who bought a shotgun and was a threat to Colorado schools had a columbine infatuation. Police say she committed suicide. We do have to think of, like, okay, I might die in my school. This senior wasn't even born in 1999 but the specter of school violence is something she and her friends have been forced to grow up with. The first day of class of the new school year, the new semester, I'll walk in and be like, okay, where are the exits? Where's the best place to hide if something happens? Reporter: Rachel Scott believes kindness and compassion can replace bullying and violence, a message she spreads today in schools around the world. She wrote, these hands belong to Rachel Joyce Scott and will some day touch millions of peoples' hearts. Reporter: It has become a columbine tradition to focus this anniversary on something positive so today many students will complete community service projects, followed by a memorial service later this afternoon. Eva.
This transcript has been automatically generated and may not be 100% accurate.