One major thing that separates the UT shooting from campus shootings of recent years is the lack of a system for alerting students or faculty to danger: Because it was the first, there was no precedent to fall back on. And say what you will about the drawbacks of being tethered to a smartphone, but imagine this: When students heard on the radio the misinformation that someone was shooting an air rifle on top of the tower, they thought something fun was going on — and some ran toward the campus, directly into the crosshairs.Other students remember thinking the pop-pop-pop of the gun, as Whitman stalked the perimeter of the tower, was someone setting off leftover fireworks from the Fourth of July. It took time for people to realize they had something to be afraid of, or to take cover. There were no emergency texts , and obviously no Twitter hashtag to check to stay up to speed about the situation. Allen Crum, who accompanied law enforcement to the top of the tower during the final showdown, remembers trying to call his wife to let her know that he was all right, only to find all the phone lines jammed.These were pre-campus-lockdown years — before anyone ever had a reason to even consider what that phrase means. As I watched the movie, it also occurred to me that this might have been the last day that anyone took their total safety for granted on a university campus. It's a sad, scary thought.But — though Tower is a sobering movie, and anyone who says otherwise clearly fell asleep about four minutes in — director Keith Maitland does a beautiful job traversing both darkness and light. His narrative doesn't shy away from painful moments, including the shame of survivors who admit they felt like cowards for not risking themselves to help save victims. But it also highlights the unlikely heroes of that day — people who did not have to step into the line of fire but did, because they couldn't just stand by and watch. The man who collected Claire from the concrete was a Vietnam veteran; later in the doc, he and Claire sit down together to talk about what happened. Fifty years after the fact, she absolves him of any lingering shame he feels about not dashing out to save her sooner.It is a profoundly touching scene — one that also serves as a reminder of how this movie isn't about the shooter: It's for the victims and the survivors, about what happened and the aftermath. It's also for new generations, who might know nothing about the clock-tower shooting but have inherited its legacy, through Columbine and Newtown, Virginia Tech and Northern Illinois University, not to mention an unbearable number of other incidents like the ones that happened on those campuses.Put another way: Tower is a film that speaks to why our breath catches when a bowling ball hits the subway tile, and why it's so hard to feel safe out in the world these days.Tower comes out in theaters on October 12, 2016. Find a screening near you