On an April morning in 1999, two teenagers walked into Columbine High School in Colorado and gunned down 13 people while wounding more than 20 others.

The image that most of us recall from that horrible day was an aerial view. It was taken of panicked students running out of the school in a single-file line, or as single-file as people can be during the worst moment of their lives.

Last Wednesday, a teenager walked into Marjory Stoneman Douglas High School in Florida and gunned down 17 people. Most of us have seen pictures and videos of the perpetrator, the mourning students, the candlelight vigils.

But if you have a high-school student, he or she has seen much more.

That's because some of the kids inside those classrooms in Florida – kids who were screaming for their lives – pulled out their phones and recorded what they saw. And then they posted it to Snapchat or to Twitter, and the recordings went viral.

This is the world in which we live. Our children don't have to imagine the horror inside, say, Columbine High or Sandy Hook or any of the other schools that have been struck by unthinkable tragedy. They see it on their phones. One clip from Wednesday's massacre shows, in 51 seconds, everything you'd rather not ever see: Crying. Panic. A dead student in the corner. Blood on the floor. Heroic police officers doing everything they can to protect and shield those kids from further physical and emotional damage.

The clip ends with the girl with her phone running from the school – which is where the Columbine footage would have started.

Every teenager with a smart phone – meaning almost every teenager – has access to these videos. So how will it affect them? Some might say it will desensitize them more than they are.

Or it could spur them to action. It could spur them to get involved in the debate over what to do about the nationwide epidemic of mass shootings.

We believe the solution is a mixture of many elements, not just one. We support the Second Amendment strongly, but we have to start discussing who needs and is allowed to have an AR-15 rifle, for example. We need to examine what certain prescription drugs are doing to the minds of young people. We need to be much more focused on improving mental-health options.

And – perhaps especially - we need to act on warnings.

Nikolas Cruz allegedly made the following comment online: "I'm going to be a professional school shooter." What other warning do we need? He spelled it out. And Broward County Sheriff Scott Israel said his agency had received more than 20 calls about Cruz in the past few years.

But this murderer, unlike the vast majority of school shooters, is still alive. It's our hope that he can provide at least an inkling into what can go so horribly wrong in a person.

So that's a difference from all of the other tragedies like it. The other difference: Before, we could look from afar at a school shooting and try not to imagine the horror inside. Today, the carnage is being recorded. And our teenagers will likely see it first.