A further report in 1945, supporting the same conclusion, was produced and stifled. In 1943, the Germans took two U.S. POWs—Capt. Donald B. Stewart and Col. John H. Van Vliet—to Katyn for an international news conference. Documents released by the National Archives and Records Administration in September 2012 revealed Stewart and Van Vliet sent coded messages to their American superiors indicating they saw proof that implicated the Soviets. Three lines of evidence were cited. Firstly, the Polish corpses were in such an advanced state of decay that the Nazis could not have killed them, as they had only taken over the area in 1941. Secondly, none of the numerous Polish artifacts, such as letters, diaries, photographs and identification tags pulled from the graves, were dated later than the spring of 1940. Most incriminating was the relatively good state of the men's uniforms and boots, which showed they had not lived long after being captured. Later, in 1945, Van Vliet submitted a report concluding the Soviets were responsible for the massacre. His superior, Major General Clayton Lawrence Bissell, General George Marshall's assistant chief of staff for intelligence, destroyed the report. Washington kept the information secret, presumably to appease Stalin and not distract from the war against the Nazis. During the 1951–52 Congressional investigation into Katyn, Bissell defended his action before the United States Congress, arguing it was not in the U.S. interest to antagonize an ally (the USSR) whose assistance the nation needed against the Empire of Japan. In 1950, Van Vliet recreated his wartime report. In 2014, a copy of a report Van Vliet made in France during 1945 was discovered.