Amnesty effected in spring 1947 did not put an end to activities of the Polish Underground fighting for Independence. Although the active underground structures were crushed by summer 1948, at the same time a phenomenon of so called return to forests became apparent. Operational measures of 'Urzad Bezpieczenstwa Publicznego' UPB (Public Security Office) used in the fight with the Underground remnants were aimed at apprehending or recruiting for cooperation its unveiled members. Because of that some of the formerly unveiled members were forced to abandon their occupations and live in hiding. Wanted/hunted by UBP they gathered in groups creating small partisan units whose purpose was an armed survival until the time of expected outbreak or war between USSR and western powers. They are referred to as so called survival groups. The use of agents web was of basic importance in UBP's anti-Underground actions. In April 1949 the Poviat UBP in Bialystok started action aiming at liquidation of a typical survival group - Corporal Gabriel Oszczapinski's 'Woodpecker' patrol, deriving from the ' Wolnosc i Niezawislosc' - WiN (Freedom and Sovereignty) Party and operating within the Bialystok Poviat territory. In the operational combination Waclaw Snarski, an agent of a code name 'Moon' , former WiN's member and sentenced by Military District Court in Bialystok to 5 years imprisonment, was used (after serving punishment, Waclaw Snarski personally applied to UBP volunteering for cooperation). The plan of operational combination prepared by the Bialystok PUBP's head Captain Antoni Pankowski assumed that the agent would make contact with 'Woodpecker', penetrate the patrol, work it out and then make partisans powerless by physical liquidation or apprehension. In result of his action, at the turn of 1949/50 three partisans died in combat, two were captured alive (later they were sentenced to death by military court and executed), the other three were arrested. Over 128 patrol's accomplices were apprehended and sentenced to long-term imprisonment.