BERLIN (AP) — An 80-year-old former officer with communist East Germany's secret police, the Stasi, went on trial Thursday over the killing of a Polish man at a border crossing in divided Berlin 50 years ago.

The defendant, whose name has not been released in keeping with German privacy rules, is charged with murder before the state court in Berlin.

He did not speak as the the trial opened, but his lawyer said that her client contests the accusations against him, German news agency dpa reported. There are no formal pleas in the German legal system.

Prosecutors announced their indictment in October.

The case goes back to March 29, 1974, when a 38-year-old Polish man allegedly took a fake bomb to the Polish Embassy to threaten officials to allow him to leave to 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 have said. After the Pole had passed the final checkpoint, the suspect allegedly shot him in the back from a hiding place.

The court has scheduled seven trial sessions through May 23.

Authorities made little headway with the case until a decisive tip on 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.