Kent State shootings

In a May 4, 1970 file photo, Ohio National Guard moves in on rioting students at Kent State University in Kent, Ohio. Four persons were killed and eleven wounded when National Guardsmen opened fire. The U.S. Justice Department, citing 'insurmountable legal and evidentiary barriers,' won't reopen its investigation into the deadly 1970 shootings by Ohio National Guardsmen during a Vietnam War protest at Kent State University. Assistant Attorney General Thomas Perez discussed the obstacles in a letter to Alan Canfora, a wounded student who requested that the investigation be reopened. The Justice Department said Tuesday, April 24, 2012 it would not comment beyond the letter. (AP Photo, File)

An overall of the Kent State campus on May 4, 1970.

In a May 4, 1970 file photo, a group of youths cluster around a wounded person as Ohio National Guardsmen, wearing gas masks, hold their weapons in the background, on Kent State University campus in Kent, Ohio. Members of the Guards killed four students and injured nine during a campus protest against the Vietnam War. The U.S. Justice Department, citing 'insurmountable legal and evidentiary barriers,' won't reopen its investigation into the deadly 1970 shootings by Ohio National Guardsmen during a Vietnam War protest at Kent State University. Assistant Attorney General Thomas Perez discussed the obstacles in a letter to Alan Canfora, a wounded student who requested that the investigation be reopened. The Justice Department said Tuesday, April 24, 2012 it would not comment beyond the letter. (AP Photo/Douglas Moore, File)

Anti-war demonstrators raise their hands toward the White House as they protest the shootings at Kent State University and the U.S. incursion into Cambodia, on the Ellipse in Washington D.C., on May 9, 1970. (AP Photo)

The water flies as young people clown a bit in the 88 degree weather during an anti-war demonstration on the Ellipse in Washington D.C., on May 9, 1970. The demonstrators were protesting the shootings at Kent State University and the U.S. incursion into Cambodia. (AP Photo)