KENT, Ohio (AP) — The Ohio National Guard opened fire on unarmed college students during a war protest at Kent State University on May 4, 1970. Four students were killed, and nine others were injured. Not all of those hurt or killed were involved in the demonstration, which opposed the U.S. bombing of neutral Cambodia during the Vietnam War.

The confrontation, sometimes referred to as the May 4 massacre, was a defining moment for a nation sharply divided over the protracted war, in which more than 58,000 Americans died. It sparked a strike of 4 million students across the U.S., temporarily closing some 900 colleges and universities. The events also played a pivotal role, historians argue, in turning public opinion against the conflicts in Southeast Asia.

In the hours immediately after the shootings, reporters at the chaotic scene struggled to determine who had fired the shots and why. Among the theories was that Guard members shot after spotting a sniper. The Associated Press reported that a highway patrol official refuted the sniper theory.