On New Year's Eve, 1944, an 18-year-old GI standing watch in a foxhole 30 miles east of the Belgian border spotted a German soldier by a narrow, moonlit river.

Unseen in the midnight, the GI, Lou Dworkin, cradled his rifle and squinted into the gunsight.

"I had plenty of time to take aim . . . did everything I was taught to do, pulled the shot and got the guy," said Dworkin, his eyes troubled as he recalled the grim encounter 71 years later. "He fell down and stayed there."

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Dworkin, now a retired social worker living in North Valley Stream, said he began shaking uncontrollably moments later, as the enormity of his first fatal wartime encounter hit home.

"I broke into a tremendous shaking fit and shivering," said Dworkin, 90. "I had never shot anyone before. People think they can walk around with a gun and shoot somebody, that it's easy; it's not. I had a sense of civilization about me. I just couldn't take it.

Dworkin said although he did not violate the rules of battle, the feeling that he had violated his own sense of humanity long lingered inside him.

"I knew it was something that had to be done, but killing is something that is against our inherent training about life itself," Dworkin said. "I haven't spoken about it for years."

Experts say even soldiers who scrupulously follow battlefield prohibition against illegal killing -- such as the targeting of civilians or the execution of prisoners -- are vulnerable to a form of psychological trauma known as moral injury whenever they take a life or cause grave injury.

"Whether it has to do with the Ten Commandments or just your humanity, you do it and you suffer," said Dr. Frank Ochberg, a psychiatrist and early pioneer of the treatment of post-traumatic stress disorder among Vietnam veterans. "Every killing is a potential for moral injury."

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Jonathan Shay, a former Veterans Affairs psychiatrist who helped develop the concept of moral injury, urges veterans grappling with battlefield guilt to share their feeling with fellow combat veterans, saying their common experience can be an incubator for healing.

But that opportunity was not immediately available to Dworkin.

Still shaking with emotion after shooting the German soldier, Dworkin had awakened a fellow soldier to tell him what he had done.

"He said, 'Don't bother me, I'm asleep. Don't talk to me about these things.' " Dworkin recalled. "He didn't care."

Dworkin said he was eventually able to make peace with himself after killing the German soldier by thinking of his grandmother. She had been among about 400,000 Polish Jews who were murdered or starved to death after Nazi leader Adolf Hitler ordered the creation of the Warsaw Ghetto in 1940.

"I carried around the guilt of shooting somebody, but ... I wanted to kill this man," Dworkin said of his battlefield encounter. "I thought because of what happened to my people and the whole world itself, I did my duty."

Nonetheless, he said he went decades without speaking of the wartime shooting. Then about 10 years ago, he joined a group of fellow veterans of the Battle of the Bulge.

"We discuss these things because it's nothing different than what the other fellow went through," Dworkin said. "There is empathy there."

When the war ended, Dworkin was a patient at a naval hospital in Queens, having suffered from severe frostbite to his hands and feet not long after the shooting incident when he encountered the arctic temperatures of early 1945.

He was discharged that year, and eventually had a 30-year career as a New York City social worker for the deaf, and retired in 1991.

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The Brownsville, Brooklyn native said he came close to himself becoming the victim of a wartime ambush.

That same winter in 1944, his sergeant had asked for volunteers to go on a patrol near the same river where he had ambushed the German soldier.

Dworkin said he stepped forward, but was refused by the sergeant, a man Dworkin said made frequent anti-Semitic remarks.

"He says I don't want any Jews, I only want men," Dworkin recalled. "I was humiliated, I was angry, I was frustrated and I was embarrassed."

Instead, the sergeant chose several other men and set off toward the river. An hour later, Dworkin heard gunfire. The patrol had walked into German crosshairs.

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"They couldn't find [the sergeant's] body at all until a few days later when they found him by the edge of the Salm River," he said, his voice dropping, his face lined with concern.

But a moment later, he brightened.

"Now the thing that I was happy about in a sense was that I was saved because of my religion, and I'm thankful for that," Dworkin said.

"I guess I must have been part of the chosen people," he said, with a twinkle in his eye. "God chose me not to go on that parade."