When: May 4, 1970.

What: On April 30, President Nixon announced the invasion of Cambodia by the U.S. and the need to draft 150,000 more soldiers for an expansion of the Vietnam War effort. Massive protests broke out on college campuses across the country.

At Kent State, protesters set fire to the ROTC building, burning it to the ground. James A. Rhodes, governor of Ohio, dispatched 900 National Guardsmen to the campus in response.

During an altercation on May 4, 28 guardsmen opened fire on a crowd. Four students were killed and nine were wounded.

Who: The four killed in the shootings were Jeffrey Glenn Miller, 20; Allison B. Krause, 19; William Knox Schroeder, 19; Sandra Lee Scheuer, 20.

Where: The actual shootings occurred in the area around Taylor Hall and the Prentice parking lot. Today, the spaces where the four students fell are marked by four sets of fence posts that light up every night.

Why: This remains to be answered. Forty-one years later there are still questions surrounding May 4, the guardsmen and a mystery FBI informant named Terry Norman. Despite new analysis of audio evidence from that day, it’s still uncertain whether the Ohio National Guardsmen were ordered to fire.

Source: Daily Kent Stater files and History.com.