View of a line of Ohio National Guardsmen, with rifles and gas masks, on the Kent State University campus as they prepare to disperse student protesters in Kent, Ohio, on May 4, 1970. The protests, initially over the U.S. invasion of Cambodia, resulted in the deaths of four protesters (and the injuries of nine others) after the National Guard opened fire on students. #

Demonstrators gather on Blanket Hill, on the Commons of Kent State University, for a student anti-war protest in Kent, Ohio, on May 4, 1970. In the background, students distribute sheets to protect themselves from tear gas. The building behind them is Johnson Hall. #

National guardsmen form a line in front of protesting students on the campus of Kent State University in this May 4, 1970, photo. In the foreground are the charred remains of the ROTC building, which had been set on fire on May 2, 1970. #

Original caption: View, from behind, as Ohio National Guardsmen in gas masks and with rifles as they prepare to advance up Blanket Hill, through clouds of tear gas, to drive back Kent State University students during an antiwar demonstration on the university's campus, Kent, Ohio, May 4, 1970. #

Original caption: Kent State University student hurls tear gas canister back towards National Guardsmen as the military is called out May 4th to put down massive anti-war protest. #

Original caption: View of students, at the base of Blanket Hill, during an anti-war demonstration at Kent State University, Kent, Ohio, May 4, 1970. Shortly after this shot was taken, four students were shot and killed by guardsmen, who opened fire at some 600 demonstrators during the incident. Among the casualties was Jeffrey Miller, seen here at center, dressed in a cowboy shirt and headband, with his thumbs in his pockets. Also visible is Mary Ann Vecchio, in dark, v-neck blouse and patterned jeans (at center right, behind the man in the t-shirt at center fore); Vecchio was later photographed crying over Miller's body in the Pulitzer prize-winning photograph that came to define the event. #

Original caption: An Ohio National Guard skirmish line advances up a hill on the campus of Kent State University, May 4, just before they turned and fired upon students participating in antiwar demonstrations. #

Original caption: As others call for help, teenager Mary Ann Vecchio (center) kneels beside the body of Kent State University student Jeffrey Miller who had been shot during an anti-war demonstration on the university campus, Kent, Ohio, May 4, 1970. #

Original caption: Kent State University student Joe Cullum (center, with beard) and others kneel on the grass beside wounded fellow student John Clearly after the latter had been shot when the Ohio National Guard opened fire on antiwar protestors, Kent, Ohio, May 4, 1970. #

Original caption: On Blanket Hill, Kent State University students, several with hands over their mouths, stare in the aftermath of the Ohio National Guard having opened fire on their antiwar demonstration, Kent, Ohio, May 4, 1970. #

Original caption: National Guardsmen are seen here on May 4, 1970, moving across the common on the Kent State campus, where four anti-war protesters were shot and killed earlier. #

Original caption: On Blanket Hill, Kent State University faculty use a microphone to try and convince antiwar demonstrators and students to disperse after the Ohio National Guard opened fire on them, Kent, Ohio, May 4, 1970. Among those pictured are Professor Glenn Frank (center, with flattop haircut) and Professor Jerry Lewis (seated at lower right side, facing camera). #

Original caption: Kent State University students disperse after an antiwar demonstration that ended when the Ohio National Guard opened fire on protesters, Kent, Ohio, May 4, 1970. #