The Soviet sentry who killed a U.S. Army officer in East Germany three years ago may have been covering his own tracks because he was away from his post. The Army's investigation into the killing reveals that Maj. Arthur D. Nicholson had been in an area guarded by the sentry for 25 minutes before he was spotted. Sources close to the investigation said the Soviet soldier may have panicked and shot Nicholson rather than face punishment if Nicholson got away.

We have reported recently on new information about this tragic event that caused a diplomatic furor in 1985. We have seen the Army's investigation, declassified at our request. Sources now tell us that the Soviet soldier was probably a frightened young sentry who was too quick on the trigger. And we have learned that the U.S. government tried and failed to have the sentry charged with murder.

Nicholson, 37, was part of a 14-member liaison team of legal spies in East Germany. Under a 1947 agreement, the United States, Britain and France are allowed to engage in legal espionage by observing Soviet military movements in East Germany. The Soviets have a similar team in West Germany. Neither side is allowed to enter restricted territory.

On March 24, 1985, Nicholson and his driver, Sgt. Jessie Schatz, were photographing a Soviet training area in the East German town of Ludwigslust. Maps provided to the Army by the Soviets showed the area as unrestricted.

The two men had been there 25 minutes, long enough for Nicholson to peer through the window of a tank shed. He was returning to his car where Schatz waited, when, according to the Army report, a Soviet guard "suddenly appeared from a proximate woodline and began firing on Nicholson and Schatz." One shot struck Nicholson in the stomach. Schatz was not hit.

Other documents revealed that the Soviet sentry was away from his post for the 25 minutes that the two Americans were there and he was startled to see them when he came out of the nearby woods, at least 80 yards away. He must have quickly calculated that he would be in trouble if he didn't stop them. Knowing that he couldn't run to the car and intercept them in time, he fired his rifle, Army intelligence analysts theorized.

The young soldier then held Schatz at gunpoint while Nicholson bled to death. Schatz was not allowed to leave for eight hours and the Soviets did not turn over Nicholson's body to the U.S. officials until the next day.

And what of the soldier who killed him?

"He could not be apprehended or interviewed as Soviet officials declined to cooperate with U.S. officials in the investigation," the Army report said.

U.S. Army commander in Europe, Gen. Glenn K. Otis, personally requested the name of the sentry from Gen. Mikhail Zaitsev, the Soviet commander in East Germany. Zaitsev refused to disclose the information at a meeting of the two generals three weeks after the shooting.

Army staffers, including Lev Yudovich, who was once a Soviet attorney, concluded that the sentry should be charged with murder.