* Friday marks 42nd anniversary of shootings
* Survivors cite digitally enhanced audio evidence
* Command to fire never proven
By Kim Palmer
KENT, Ohio, May 3 (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.
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 (75 metres) 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.
A Justice Department official closed the matter last month, finding the recordings were still inconclusive.
Canfora, and other wounded students Dean Kahler, Thomas Grace and Joe Lewis, asked Holder on Thursday for a new probe, saying anyone involved in the shooting should be offered immunity to provide information. They asked any surviving guardsmen to come forward with information.
"I was an angry young man for a number of years," Canfora said. "We have to work within the system. I've learned a lot since we were younger. I believe they were ordered to shoot us."
Kahler, who has been paralyzed from the waist down since the shooting, told Reuters: "We want justice in a sense, to have the truth. It would be nice to know what actually happened.
If the United States does not open a new investigation, the May 4 group plans to appeal to the International Court of Justice, the U.N. Human Rights Council or the Inter-American Court of Human Rights Canfora said.
(Reporting by Kim Palmer; Editing by David Bailey and Peter Cooney)