Presentation of the first interdisciplinary research on Szlamek (Szlama Winer), his family and his social (underground) circle. Collation of the existing knowledge about the author of the testimony on the Holocaust in Wartheland (“Szlamek’s testimony”, the “Grojanowski Report”) in the context of its importance for the Warsaw ghetto underground and the Polish Underground State, but the refugee’s genealogy well-documented in sources. The author has examined and analyzed the existing information on the compulsory gravedigger in the extermination center at Kulmhof, and compared the extant literature with archive research results, which makes it possible to broaden our knowledge of the most enigmatic conspirators of the Holocaust era as well as his closest relations. The historical and biographical investigations undertaken here and, consequently, verified, methodologically prepared historical data are to eliminate not only the spelling of the witnesses’ name accumulated and notoriously repeated errors in Holocaust historiography, but they are to serve as a supplement to the existing biographical entry, barely outlined on the basis of a surviving testimony and a fragment of the Warsaw–Zamość correspondence kept in the “Ringleblum Archive”