U.S. refuses request to probe 1970 Kent State shooting CLEVELAND (Reuters) - The U.S. Justice Department refused to reopen an investigation into the deadly 1970 shooting of student protesters at Kent State University, one of the seminal moments of the anti-Vietnam war movement, saying new audio evidence of an order to fire was inconclusive. Kent State students were protesting the war in Vietnam and the U.S.-led invasion of Cambodia when Ohio National Guard troops opened fire, killing four students and wounding nine others. Afterward, student strikes closed down schools across the nation, and divisiveness intensified over the war. Assistant U.S. Attorney General Thomas Perez sent a letter to Alan Canfora, one of the wounded students and now the director of Kent May 4 Center, saying the department was "unable to re-prosecute this case." Canfora requested the reinvestigation after discovering a copy of a 29-minute recording from Kent State student Terry Strubbe, who recorded the demonstration on a reel-to-reel machine from his dormitory room. A digital enhancement of the recording appeared to reveal "a verbal command to fire," followed by 12.5 seconds of firing, Canfora said. The volleys were preceded by what sounded like four gunshots, possibly from a handgun, he said. This is the most significant discovery in the investigation. It has always been the central question: was there a command to shoot? Canfora said in an interview on Tuesday. "Only now through modern digital technology can we finally answer that question," he said. Canfora asked the Justice Department in 2010 for a new investigation in light of the audio evidence. Eight guardsmen were originally charged in October 1974 with depriving the students of their civil rights. But after the prosecution presented its case, U.S. District Judge Frank Battisti granted the defendants' motion for acquittal, ruling the government had not proven the charges. In a letter to Canfora dated April 19, Perez wrote that there were too many legal hurdles to overcome to reopen the case. He said the legal bar against double jeopardy prevents a retrial of those who had already been acquitted, and the statute of limitations had run out on possible charges. Some of the guardsmen had passed away, he added. As for Strubbe's tape, Perez said the government's analysis concluded the four thuds heard before the National Guard volleys were likely the dorm room door closing as people came and went, and it was impossible to discern the command amid the shouting. "Examiners found the quality of the audio recordings to be poor and found that the distortion, frequency response, and low quality microphone used to make the recording rendered the audio quality insufficient for gunshot analysis," Perez's letter said. Canfora said he was not looking to prosecute individual guardsmen but wanted instead "a historical pronouncement of truth about the massacre at Kent State." He said he upset it took two years to decide not to go forward. "We have modern digital forensic science on our side," he said. Six of the seven surviving victims of the Kent State shooting plan to announce on May 3, the day before the event's 42nd anniversary, an effort to move the case to an international court. A Justice Department spokesman had no comment. "If our Federal and State governments do not provide truth, justice, healing and reconciliation, you will be responsible for motivating our further actions in and out of courts, on the local, state, national and international levels," Canfora wrote in a response to Perez. Additional reporting by Jeremy Pelofsky in Washington; Editing By Andrew Stern and Jackie Frank