The historians who unearthed the 17 volumes of files that revealed Mr. Kurras’s double life say there is no evidence to support the theory that the Stasi was behind the killing. Berlin officials have resisted public calls from victims’ groups and others to retry Mr. Kurras. He was acquitted in 1967, the year of the shooting, of manslaughter charges and was later allowed to rejoin the police force after the verdict was upheld.

In an interview with the Bild, Mr. Kurras, 81, confirmed that he had been in the East German Communist Party. “Should I be ashamed of that or something?” Mr. Kurras was quoted as saying. As for the Stasi, he said, “And what if I did work for them? What does it matter? It doesn’t change anything,” the paper reported.

Mr. Kurras does not deny that he shot the demonstrator, Benno Ohnesorg, in the back of the head, but has said the shooting was an accident. He denied records showing he had been paid by the security service, and said the agents who had put those details in his file must have been lining their own pockets.

Mr. Kurras was born in East Prussia and volunteered for military service in 1944 when he was 16 years old. He was imprisoned not long after the war by the Soviets at the Sachsenhausen concentration camp for three years. He was known to be an enthusiastic gun collector and an excellent marksman.

Image The East German Communist Party membership card of Karl-Heinz Kurras, a former West Berlin police officer who also acted as a Stasi spy for East Germany. Credit... Fritz Reiss/Associated Press

He began leading a secret double life in 1955, when he went to the authorities in East Berlin and asked to move to East Germany and join the police there. Instead, according to files unearthed by the historians Helmut Müller-Enbergs and Cornelia Jabs, he was told to stay with the police in West Berlin while spying for the Stasi, and he had a cover name, Otto Bohl.

If Mr. Kurras seemed to fit the bill of the “fascist cop,” Mr. Ohnesorg came across as the most innocent of victims. A student who also wrote poetry, he was married, his wife pregnant with their first child, when he went to a demonstration against a state visit by Iran’s leader, Shah Mohammed Reza Pahlavi.