BERLIN (AP) — An 80-year-old former officer with communist East Germany’s secret police, the Stasi, was sentenced Monday to 10 years in prison for the murder of a Polish man at a border crossing in divided Berlin 50 years ago.

The Berlin state court said in its ruling that there was no doubt that the then-first lieutenant shot the 38-year-old Polish citizen Czesław Kukuczka in an ambush on March 29, 1974 on behalf of the East German secret police, German news agency dpa reported.

“It was not the act of an individual for personal reasons, but planned and mercilessly executed by the Stasi,” presiding judge Bernd Miczajka said in his sentencing remarks. He said the defendant, whose name was not given in line with German privacy rules, fired the shot “at the end of a chain of command,” dpa reported.

The court fell short of the Berlin public prosecutor’s request for 12 years in prison. The accused’s defense lawyer had demanded an acquittal. According to lawyer Andrea Liebscher, it had not been proven that her client fired the fatal shot, dpa reported.

The defendant remained silent in court but his lawyer said at the beginning of the trial that he denied the allegations. The verdict can still be appealed.

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The case goes back to March 29, 1974, when Kukuczka allegedly took a fake bomb to the Polish Embassy to threaten officials to allow him to leave for West Berlin, and the Stasi decided to pretend it was authorizing his departure.

He was provided with exit documents and accompanied to a border crossing at the Friedrichstrasse railway station in East Berlin, according to prosecutors.

The defendant — who was 31 at the time — was tasked with rendering the Polish man “harmless,” prosecutors said. After the Pole had passed the final checkpoint, the suspect allegedly shot him in the back from a hiding place.

Authorities made little headway with the case until a decisive tip-off about the identity of the shooter emerged in 2016 from the Stasi’s voluminous archives, dpa reported. Prosecutors initially suspected the case would amount to manslaughter, which unlike murder falls under the statute of limitations in Germany.

East Germany built the Berlin Wall in 1961, preventing most of its citizens from traveling to the West. Many tried to escape by tunneling under it, swimming past it, climbing or flying over it. At least 140 people died in the attempt.

The heavily fortified border was opened on Nov. 9, 1989, a key moment in the collapse of communism in Europe. Germany was reunited less than a year later.