On August 1, 1966, a sniper climbed the steps of the University of Texas at Austin's 27-story tower. Seventeen people were killed and more than 30 others were injured. Fifty-six years later, mass shootings make headlines nearly every week. And the University of Texas tower looms over campus, a reminder of one of the first mass school shootings in United States history that has long been forgotten.

In season four of "Darkness," host Sara Kinney walks through the day of the University of Texas Tower shooting and outlines its legacy among the decades-long epidemic of gun violence in schools. Hear from survivors, heroes and family members about their day in 1966, their lives since then and the state of gun control today.