For most of us, it's hard to know the heartbreak of parents who have lost children to school shootings.
It's harder still to know the terror the victims felt in their last violent moments, or to feel the weight of memory that each survivor carries.
Yet, there is no safety in what we don't know. School shootings are agonizingly frequent. They happen in some of America's safest neighborhoods and every one of us is at risk of bearing close witness to such tragedies.
Too often, our memories of the details of the deaths and sorrow seem to drift away.
Here's a remembrance of some of the worst school shootings in recent times, and some of the brave people who tried to protect the innocent from modernity's worst moments of senseless mayhem.
Sparks Middle School: It's estimated up to 30 children witnessed the deadly shooting at this school east of Reno, Nevada, where a 12-year-old boy gunned down a teacher and injured two students on Monday.
Authorities are still investigating the incident, but early reports say 45-year-old math teacher Michael Landsberry was trying to stop the boy from killing anyone when he was shot and killed. A former Marine and Air National Guard member, Landsberry had served and survived two tours in Afghanistan before facing death at the hands of an armed child on American soil.
His wife told the Reno Gazette-Journal that his altruism didn't come as a shock.
"To hear he was trying to protect those kids doesn’t surprise me at all," Chanda Landsberry said. "He could have ducked and hid, but he didn’t. That’s not who he is."
Sandy Hook Elementary School: On December 14, 2012, a suicidal gunman killed 26 people while school was in session in Newtown, Connecticut. Twenty of them were first graders—small children who held hands and begged for their lives in some instances. Shooter Adam Lanza also gunned down six adults before killing himself.
Teacher Kaitlin Roig hid in the bathroom with 14 of her students, begging them to be quiet and pray and think happy thoughts.
Days away from the holiday recess, students told her, "I just want Christmas... I don't want to die, I just want to have Christmas," as they huddled into the space where she'd blocked the door with a cabinet.
Students asked Roig if they could go out to see if anyone was still there after gunfire went silent, but Roig was so protective of the children, she refused to even let officers in, telling police to slide a badge under the door when they came to the rescue.
Virginia Tech: Thirty-two students and faculty were killed on the small campus in Blacksburg on April 16, 2007 when Seung-Hui Cho, who was mentally ill, opened fire on campus. Cho had exhibited bizarre behavior, stalking two women and writing tortured rants in English classes, but had not received adequate medical attention.
Holocaust survivor Liviu Librescu, 75, was teaching his mechanical engineering class that morning when gunfire erupted in the building. The professor, small in stature but big in courage, stayed behind to block the door and stop Cho from getting into his popular class. He was gunned down by Cho, but about 20 students survived because of his bravery.
Senior Caroline Merrey, says Librescu shouted for students to hurry and escape through windows while gunfire rang out in the hall. She says she owes her life to him.
Santa Monica College: Six people were killed on June 7 after a domestic dispute at a home near campus grew into a shooting rampage when John Zawahiri came to the seaside campus in Southern California, where he fired at least 70 rounds with his AR-15 style rifle in 13 minutes. Law enforcement said the death toll could have been much worse.
But the shooter didn't drive himself to campus that day.
Debra Lynn Fine saw Zawahiri carjack a woman and tried to stop him. The 50-year-old mother of two could have ignored the man pointing a weapon, but instead drove toward danger, looked him in the eye and yelled at him to stop. He opened fire, injuring her with multiple shots but she survived—and law enforcement believe she distracted the shooter from killing the woman he was carjacking.
She's one of the few people who lived to tell the tale of what it was like, facing a cold-blooded killer.
"It was the first time I’d ever seen somebody who was so intent and present and cold. He was just a robot. He’s emotionless. Very intense, very cold and just on a mission. On a mission to kill as many of us as of as he could.”
Northern Illinois University: It was Valentine's Day when Steven Kazmierczak walked into an Intro to Ocean Science class on the Dekalb campus. Witnesses say he just sood there looking at the class for a moment before opening fire on the front row with a shotgun.
In the chaos, students ran and Kazmierczak reloaded. He fired six shotgun loads before switching to a Glock to fire 48 more rounds at students, as they tried to get out of exits that were blocked with the crush of human panic.
Five people were killed and more than 15 others were injured before the shooter took his own life.
One victim, 20-year-old Dan Parmenter wasn't even enrolled in the class that day—he was just sitting in the front row to keep his girlfriend company ahead of celebrating with his Valentine. He died trying to shield Lauren Debrauwere from bullets, and she survived.
When Debrauwere awoke in a hospital intensive care unit days later, having suffered gunshot wounds to the hip and abdomen, she was unable to ask because of a tube in her throat, but wrote "Dan?"