He did not know about the murder by gas, repeating the common belief at the time that deported Jews were being exterminated with electricity.[5] Karski met with the Polish government-in-exile, including the Prime Minister, Władysław Sikorski, as well as with members of political parties such as the Socialist Party, National Party, Labor Party, People's Party, Jewish Labour Bund and Zionist Party. He also spoke to Anthony Eden, the British Foreign Secretary, and included a detailed statement on what he had seen in Warsaw and in Bełżec. In 1943 in London he met the author and journalist Arthur Koestler.