According to the Lithuanian historian Bubnys who cited the Polish historian Helena Pasierbska, during 1941–1944, approximately 108 men were members of YB.
In 1942, he witnessed the Ponary massacre of some 100,000 mostly Polish Jews by German SD, SS and the Lithuanian Nazi collaborators Ypatingasis būrys, which he described in his 1969 book Nie trzeba głośno mówić (One Is Not Supposed to Speak Aloud).