Four of the Kent State students wounded by Ohio National Guard gunfire on May 4, 1970 that left four of their fellow students dead want U.S. Attorney-General Eric Holder to order a new inquiry into the tragedy.
The soldiers said they fired in self-defence, not at a command to fire. Now the survivors claim that digitally-enhanced audio proves the officer in command did order his troops to fire on the student protesters.
A command to fire has never been proven and guardsmen said they fired in self-defense. Criminal charges were brought against eight guardsmen, but a judge dismissed the case. Wounded students and families of those slain later received a total of $675,000 after civil lawsuits.
The shootings also spawned an investigative commission, numerous books and Neil Young's song, "Ohio," which became an anti-war anthem. A Pulitzer Prize-winning photograph of a teenage girl kneeling over the body of one of the slain students became an enduring image of the tragedy.
In 2010, Alan Canfora, one of the wounded students and director of the nonprofit Kent May 4 Center, asked the Justice Department to review the enhanced recording, which was taken 250 feet from the guardsmen when they fired their shots in 1970.
Canfora and other audio specialists say the enhanced recording shows a clear military order to fire seconds before the shooting. The troops fired 67 shots over 13 seconds.