FILE – 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)