They extorted hush money from various Ghetto craftsmen. They arrested Jews and released them in return for thousand of zlotys in ransom money.. “The Thirteen” created an atmosphere that encouraged informant activity, which became the scourge of the Ghetto. Some even called them “The Jewish Gestapo”. Gutman, Joseph Kermish, and Israel Shaham, who edited Ringelblum’s diaary, said in no uncertain terms: “This office was essentially a Jewish Gestapo division”.
Page 96, Walls Around: The Plunder of Warsaw Jewry During World War II and Its Aftermath, Itamar Levin