I'm trying to think if I can remember a time we could accept the official version of anything without question. Now we can add another to the list of revised histories with this explosive story:

The Ohio National Guardsmen who fired on students and antiwar protesters at Kent State University on May 4, 1970 were given an order to prepare to shoot, according to a new analysis of a 40-year-old audio tape of the event.

"Guard!" says a male voice on the recording, which two forensic audio experts enhanced and evaluated at the request of The Plain Dealer. Several seconds pass. Then, "All right, prepare to fire!"

"Get down!" someone shouts urgently, presumably in the crowd. Finally, "Guard! . . . " followed two seconds later by a long, booming volley of gunshots. The entire spoken sequence lasts 17 seconds.

The previously undetected command could begin to explain the central mystery of the Kent State tragedy - why 28 Guardsmen pivoted in unison atop Blanket Hill, raised their rifles and pistols and fired 67 times, killing four students and wounding nine others in an act that galvanized sentiment against the Vietnam War.

The order indicates that the gunshots were not spontaneous, or in response to sniper fire, as some have suggested over the years.

"I think this is a major development," said Alan Canfora, one of the wounded, who located a copy of the tape in a library archive in 2007 and has urged that it be professionally reviewed. "There's been a grave injustice for 40 years because we lacked sufficient evidence to prove what we've known all along - that the Ohio National Guard was commanded to kill at Kent State on May 4, 1970."

This excerpt from a copy of Terry Strubbe's Kent State recording contains the order for the Guard to prepare to fire. The word "Guard!" can be heard at 9.3 seconds. "All right, prepare to fire" begins at 19.5 seconds. "Get down!" is spoken at 22.3 seconds. The final "Guard!" is at 23.7 seconds, and the gunshots begin at 26 seconds.