Karski met with Polish politicians in exile including the Prime Minister , as well as members of political parties such as the Socialist Party , National Party , Labor Party , People 's Party , Jewish Bund and Poalei Zion . He also spoke to the British Foreign Secretary Anthony Eden , giving a detailed statement on what he had seen in Warsaw and Bełżec . In 1943 in London he met journalist Arthur Koestler , author of '' Darkness at Noon '' . He then traveled to the United States , and on 28 July 1943 Karski personally met with President Franklin D. Roosevelt in the Oval Office , telling him about the situation in Poland and becoming the first eyewitness to tell him about the Jewish Holocaust . During their meeting , Roosevelt asked about the condition of horses in Poland . Roosevelt did not ask one question about the Jews . Karski went on to meet with many other government and civic leaders in the United States , including Supreme Court Justice Felix Frankfurter , Cordell Hull , William Joseph Donovan , and Rabbi Stephen Wise . Frankfurter , skeptical of Karski 's report , said later " I did not say that he was lying , I said that I could not believe him . There is a difference . " Karski presented his report to media , bishops of various denominations ( including Cardinal Samuel Stritch ) , members of the Hollywood film industry and artists , but without much result . His warning about the Yalta solution and the plight of stateless peoples became an inspiration for the formation of the Office of High Commissioner for Refugees after the war
Yalta solution
Yalta Conference
Jan Karski