Siemiaszko's first research project based on witness accounts related to the Volhynian massacres of Poles began in mid 80s.
Subsequently, Władysław with daughter Ewa Siemaszko, in their own ten-year-long research project went on to document murders committed on Polish citizens by Ukrainian Insurgents in some 1,865 villages and towns of Volhynia during the Nazi and Soviet occupations.