While walking home from a convenient store, 17-year-old Trayvon Martin was shot and killed by George Zimmerman, a neighborhood watch volunteer. The incident jump-started the Black Lives Matter movement and sparked outrage across America. The incident mirrored the racial violence against 14-year-old Emmett Till in Mississippi 57 years earlier and modern-day lynching. Pictured: A demonstration in Washington on July 20, 2013, following the acquittal of George Zimmerman. (Joe Raedle // Getty Images)