A 93-year-old former guard at the Nazi Stutthof concentration camp has testified at his trial that he once saw people being led into the gas chamber, followed by screaming and banging sounds behind the locked door.

Bruno Dey, a former SS private, went on trial on 17 October at the Hamburg state court where he stands accused of having been an accessory to the murder of 5,230 people while he was deployed at Stutthof from 1944 to 1945.

Asked on Friday by the presiding judge what exactly he saw from his sentry’s watchtower, Dey replied: “That people were led in, into the gas chamber, then the door was locked,” the news agency DPA reported.

He said he heard screams and banging shortly after, but added: “I didn’t know that they were being gassed.”

Dey said that about 20 or 30 prisoners were led in, and that they didn’t resist. He couldn’t say whether they were men or women, because their heads were shaved, or whether they were Jews or other prisoners. He also couldn’t say what happened afterwards. “I didn’t see anyone come out.”

On another occasion, he said, he saw a group of 10 or 15 men being led into the gas chamber, but they then came out and were taken to the crematorium building by people in white overalls. He said he heard that the prisoners were supposed to work outside the camp and had to be checked first.

Dey said he and around 400 other soldiers were taken to Stutthof in June or July 1944 and he did not know at the time what kind of people were incarcerated there. He said he heard only “rumours” that they included political prisoners and Jews.

Though there is no evidence that Dey was involved in a specific killing at the German camp near Danzig – today the Polish city of Gdańsk – prosecutors argue that as a guard he helped the camp function.

Despite his age, Dey is being tried in a juvenile court because he was 17 when he started serving at Stutthof.

He faces six months to 10 years in prison if convicted. There are no consecutive sentences under German law.