But the case was reopened when a former Nazi trainee, Hungarian-born Adalbert Lallier, decided to break half a century of silence to reveal that he had witnessed the killings.
Julius Viel was convicted of murdering seven Jewish prisoners at a concentration camp in Nazi-occupied Czechoslovakia.
Viel, who had denied the charges, sat impassively as the verdict was read out. He is thought to be one of the last Nazis likely to stand trial.
His lawyer said he would appeal, as evidence presented to the court had been contradictory. His legal team had told the court he was stationed in Vienna at the time of the murders.
"I'm sorry for my wife's sake," Viel told journalists after the hearing.
Viel, who worked as a journalist after the war, was a second lieutenant in the SS at the time of the crimes.
The Jewish people who died were inmates at the Theresienstadt concentration camp, killed in the spring of 1945.
They were digging anti-tank trenches at Leitmeritz, near the camp, when they were killed.
Viel had been investigated for the murders in the 1960s, but the case was closed after a lack of evidence.
But the case was reopened when a former Nazi trainee, Hungarian-born Adalbert Lallier, decided to break half a century of silence to reveal that he had witnessed the killings.
Mr Lallier, an economics professor in Canada, told the court in Ravensburg that Viel had shot the victims in cold blood.
He was the only person to give evidence, but the German judge said he had believed his account.
"Lallier certainly did not imagine what happened," said Judge Hermann Winkler.
He said Viel had escaped a life sentence because of the time which had elapsed since the crime.
But he said Viel's exemplary life after the war - which included winning government acclaim for some of his work - did not reduce the enormity of his original crime.
"At the beginning of this life's journey, there were seven deaths," said Judge Winkler. "The killing of a human was a crime then as well. The defendant knows it wasn't animals but people he did away with."
Around 360 witnesses in Germany, Austria, Britain and Canada were interviewed in a two-year investigation into the case.
A number of other investigations into Nazi killings have been continuing, but most defendants are now considered too old or too ill to stand trial.