WARNING: GRAPHIC CONTENT - Hitler's 'special execution group' rounded up patients and doctors from psychiatric hospitals such as the one in Owinska (main) and took them to Concentration Camp Poznan (bottom left), the first place the Nazis experimented with lethal gas. They seized the 19th Century fort -once known as Fort Colomb - in October 1939. Three trucks carrying 25 people left the hospital every day and took them to primitive gas chambers (top right) which had formerly been used as an artillery depot. Once the men had been killed, the SS began taken the female patients and eventually the children. By November, all the patients were dead. The Nazis also used mobile gas chambers (bottom right) in specially adapted vans to kill patients from other hospitals in the area. By mid-1940, more than 5,000 patients and hundreds of Poles had been gassed to death at the camp.