In Warsaw, the collaborationist groups Żagiew and Group 13, led by Abraham Gancwajch and colloquially known as the "Jewish Gestapo", inflicted considerable damage on both Jewish and Polish underground resistance movements. Over a thousand such Jewish Nazi collaborators, some armed with firearms, served under the German "Gestapo" as informers on Polish resistance efforts to hide Jews, and engaged in racketeering, blackmail, and extortion in the Warsaw Ghetto. A 70-strong group led by a Jewish collaborator called Hening was tasked with operating against the Polish resistance, and was quartered at the Gestapo's Warsaw headquarters on "ulica Szucha" (Szuch Street). Similar groups and individuals operated in towns and cities across German-occupied Poland — including Józef Diamand in Kraków and Szama Grajer in Lublin. It is estimated that at the end of 1941 and the start of 1942 there were some 15,000 "Jewish Gestapo" agents in the General Government.