At the beginning of 1944, Ron Jeffery, an agent of British and Polish intelligence in occupied Poland, eluded the Abwehr and travelled to London with a report from Poland to the British government. His efforts were at first highly regarded, but subsequently ignored by the British, which a disillusioned Jeffery later attributed to the treachery of Kim Philby and other high-ranking communist agents entrenched in the British system. Jeffery tried to inform the British government about the Katyn massacre, but was as a result released from the Army.In 1947, the Polish Government in exile 1944-1946 report on Katyn was transmitted to Telford TaylorIn the United States a similar line was taken, notwithstanding two official intelligence reports into the Katyn massacre that contradicted the official position. In 1944, Roosevelt assigned his special emissary to the Balkans, Navy Lieutenant Commander George Earle, to produce a report on Katyn. Earle concluded the massacre was committed by the Soviet Union. Having consulted with Elmer Davis, director of the United States Office of War Information, Roosevelt rejected the conclusion (officially), declared he was convinced of Nazi Germany's responsibility, and ordered that Earle's report be suppressed. When Earle requested permission to publish his findings, the President issued a written order to desist. Earle was reassigned and spent the rest of the war in American Samoa.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.

Question: What are the full names of the two U.S. POWs taken to Katyn by the Germans for an international news conference?
Answer: Donald B. Stewart, John H. Van Vliet