During the occupation, the Germans re-organised the Polish police forces. The regular police, henceforth known as ‘blue police’, resumed its duties under the supervision of the German Order Police [Orpo – Ordnungspolizei], while the secret police, now called Polish Criminal Police, was incorporated into the German Kriminalpolizei, or Kripo. Although there have been no historical studies of the Polish Kripo, it seems that this organisation played an essential role in tracking down and killing the Jews in hiding. This article, which largely draws on previously unknown archival material, focuses on the Warsaw section of the Polish Criminal Police. More specifically, it discusses the creation and the role of several specialised units, created for the sole reason of hunting down the Jews in hiding, in Warsaw, during the 1943–1944 period. The units have been responsible, among others, for the detection and arrest of Emanuel Ringelblum, the founder of “Oneg Shabbat”, the underground archive of the Warsaw ghetto.