On September 26, 1908, Prystor was one of the participants of the legendary Bezdany raid. At the same time, he was actively involved in the activities of the Union of Active Struggle. On March 28, 1912 in Warsaw, Prystor was arrested by the Okhrana. After two years of imprisonment in Warsaw Citadel, he was in 1914 sentenced to 7 years of exile, and sent to the prison in Oryol. Released after the February Revolution (March 17, 1917), he continued working for the Polish Socialist Party.