On September 2, 1955, a metal casket containing Emmett Till’sbloated and broken body arrived in Chicago. Less than two weeks before, Till, a fourteen-year-old African-American boy, had travelled down to Mississippi to visit relatives, a summer sojourn made by many children of the Great Migration. On August 24th, Till, along with some of his cousins and friends, had stopped in at Bryant’s Grocery & Meat Market, where Till allegedly spoke to Carolyn Bryant, a twenty-one-year-old white woman, who was working behind the store’s counter.

More than sixty years later, we still do not know what, exactly, happened in that store. Some say that Till, a child of the North who was unfamiliar with Southern racial etiquette and social customs, said “goodbye” to Bryant without the requisite “ma’am.” Others say that Till wolf-whistled at Bryant, or that his lisp somehow made it sound as if he had whistled. A few days later, Till was abducted from his great-uncle’s home by Bryant’s husband, Roy Bryant, and Roy’s half-brother, J. W. Milam. Three days after that, Till’s body was found in the Tallahatchie River. He had been brutally beaten, shot in the head, and thrown in the water with a hundred-pound metal fan tied around his neck with barbed wire. He was murdered a month after his fourteenth birthday.

Back in Chicago, Till’s mother, Mamie Till Bradley, received his body and decided to have an open-casket funeral. “Let the people see what I’ve seen,” she told the funeral-home owner. On the day of the funeral, thousands of mourners lined up in the streets near the Roberts Temple Church of God, waiting for hours to reach the casket. Inside, people shrieked, wailed, and fainted. They were unprepared for what they saw: Till’s right eye was missing and his face was disfigured beyond recognition. Photographs were taken, and the black pressdisseminated the image of Till’s mutilated corpse far outside of Chicago, making Till’s death a national story. In the years that followed, many civil-rights activistswould say that Till’s murder had been what spurred them to join the movement.

“Stay with me.” Those were the words Diamond Lavish Reynolds used just a few weeks ago to implore her Facebook friends and followers to witness a horror scene. She was live-streaming a video to Facebook with her phone. As she panned her phone’s camera to her left, viewers saw blood on the shirt of her fiancé, Philando Castile, a cafeteria manager at a Montessori school in St. Paul, Minnesota. He was slumped toward Reynolds, moaning audibly, bleeding to death. Reynolds narrated, telling the audience that Castile’s arm had been nearly “shot off” by the police officer who had stopped them for a broken taillight. Reynolds’s video did not show the police officer’s face, but his gun, pointed into the car, was caught squarely in the frame.

Like Mamie Till Bradley, Reynolds made a decision to share her tragedy with the world. Viewers watched as Castile’s life slipped away, while the officer who shot him barked directions at Reynolds. We watched as she followed those directions, remaining heroically calm before coming to the heartbreaking realization that Castile had died. In the days and weeks that followed, millions watched Reynolds’s video and relived the last moments of Castile’s life.

For the past eight years, I’ve taught American history to college undergraduates. Early in my teaching career, I made a conscious choice not to include photographs of lynchings in my course materials. Anytime my lesson plan included a discussion of lynchings, I would prepare a stack of index cards, each with the name of a lynching victim on it, and give one to each student as he or she entered the classroom. I would ask the students to say the names of the people on the cards, and I would explain that these were among the reported thirty-four hundred and forty-six men and women who were lynched in America between 1882 and 1968. I thought that this might be a more solemn and respectful way to honor those who had been murdered. My concern was that, if we merely looked at photographs of lynchings, we risked being complicit in those terrible acts, in their attempts to rob their victims not just of life but also of dignity, honor, and, above all, privacy. I worried that we couldn’t help but be voyeurs, observing spectacles rather than bearing witness to atrocities.

Over the past two years, as videos of black men being killed by police became national news with terrible frequency, I took a similar position. “Why should we look at these videos?” I wondered. The facts of these killings should have been enough to spark outrage and action. Were we becoming inured to seeing black suffering and death? But Diamond Reynolds’s act of heroism, and the conversation it prompted, made me reconsider my stance.

In the days after Castile’s death, I was listening to NPR’s “Code Switch” podcast and heard a reporter’s interview with a man named Joe Jones, an African-American resident of Dallas. Jones said that, after Castile’s death, his conversations with white acquaintances had been different from those he had had after past incidents of police violence. Jones believed that those who had previously been willing to accept violence as “just a natural part of policing” had begun to “feel and empathize in a way that” Jones had “never seen before.” Perhaps it was that Reynolds and her four-year-old child had been present in the car with Castile, Jones said, or that Castile had a permit to carry the gun he had told the officer was in the car with them. “Folks who I’d never seen sympathize with a young black man who’d been shot by a cop were able to say, for the first time, ‘I can see myself in that position,’ ” Jones said. Reynolds’s courageous act helped make this possible. She had “let the people see what I’ve seen,” as Mamie Till Bradley had put it.

Mamie Till Bradley and Diamond Reynolds both shared their sorrow with the world. They asked onlookers to view the bodies of two black men and see a son, a brother, a boyfriend, a loved one. Looking is hard. It shakes us and haunts us, and it comes with responsibilities and risks. But, by allowing us all to look, Bradley and Reynolds offered us real opportunities for empathy. Bradley’s moral courage galvanized a generation of civil-rights activists. We have yet to see how far Reynolds’s bravery will take us.