KENT, Ohio (Reuters) - Survivors of the shooting of 13 students by the Ohio National Guard during an anti-war demonstration at Kent State University in 1970 called on Thursday for a new probe into the incident that came to define U.S. divisions over the Vietnam War.

Four students were killed and nine wounded in the shootings on May 4, 1970 that followed days of demonstrations on the campus after disclosures of a U.S.-led invasion of Cambodia that signaled a widening of the war in Southeast Asia.

Kent State was shut for weeks after the shootings and student strikes closed down schools across the nation.

On the eve of the 42nd anniversary of the shootings, four students wounded that day asked U.S. Attorney General Eric Holder to investigate digitally enhanced audio evidence they believe proves an officer ordered the guardsmen to fire on the unarmed students....