On 7 October 1955 Seifert married Renata Urszula and reportedly fell apart when she died of an embolism during premature birth on 11 February 1961. Holding the doctors responsible for the death of his wife he wrote a 120-page letter titled "Muttermord — Einzelschicksal und Analyse eines Systems" (Matricide - Individual fate and analysis of a system), and sent it to agencies, doctors and pharmaceutical manufacturers. Therein he tried to prove that the treatment of his wife's embolism was done wrong, called society a criminal system and equated doctors with murderers, writing: