By Rick Sallinger

LITTLETON, Colo. (CBS4) – Tom Mauser’s face has become familiar over the years, but more familiar are the shoes he wears. They are his son’s. Daniel Mauser was one of the 12 Columbine students who lost their lives. His father Tom still wears them in his memory.

Daniel Mauser (credit: CBS)

Twenty years after the shootings that left 12 students and one teacher dead, Tom recalled what got him started on the road he decided to take.

CBS4’s Rick Sallinger interviews Tom Mauser. (credit: CBS)

“I think the main guiding thing for me was wanting to honor Daniel,” he told CBS4’s Rick Sallinger.

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He honors his son with his activism. His cause is to carry on with the gun control issues he and his son had discussed.

“I just blew it off, then two weeks later he was killed with one of those guns purchased through a loophole in the Brady bill,” Tom said.

He started by helping to close Colorado’s gun show loophole which allowed firearms sales without background checks. On Nov. 7, 2000, Colorado voters overwhelmingly passed Amendment 22. Tom Mauser took to the stage to celebrate in honor of his son.

“We did it.. wow! wow!” he said at the time.

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Mauser has taken his crusade to the offices of the National Rifle Association where he has twice been arrested.

Mass shootings at schools have not stopped, but what happened at Columbine has provided lessons learned. Officers now arriving at the scene of such an incident are often instructed to confront the gunmen rather than wait outside for SWAT teams to arrive.

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“The whole world has changed for us in terms of school safety,” said John McDonald who heads security for Jefferson County schools. That world, he explained, starts with threat assessment.

Sallinger interviews John McDonald. (credit: CBS)

“We have an incredibly robust crisis mental health unit that this year has seen a significant increase in suicidal ideation,” Mc Donald said.

Students or anyone can call Safe2Tell, the anonymous tipline that came as a result of Columbine.

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McDonald said what happens next is “We triage it, investigate it and get the student back to learning.” The hotline and app have been credited with preventing numerous acts of violence.

There are other measures, too. Where once there were only fire drills, now there are active shooter drills at schools across the country.

Law enforcement officers take part in an active shooter drill. (credit: CBS)

“These are important opportunities to prepare students for threats of our times in our environment,” the McDonald noted.

Twenty years on, Columbine’s impact on school security is profoundly felt today.

Rick Sallinger