Zych took part in various resistance activities, among them, serving as a secret courier for right wing political organisation KPN.
After being accused and sentenced for his alleged involvement in the Zdzisław Karos case, between 1982–1986, he was imprisoned by the Communist regime.
The body of Sylwester Zych was found at night on July 11, 1989, at a bus stop in Krynica Morska.
The circumstances surrounding the deaths of three Polish priests (Sylwester Zych, Stefan Niedzielak, and Stanisław Suchowolec) were later investigated by a Senate commission composed of Zbigniew Romaszewski (chairman) and Alicja Grześkowiak (vice chairman).
The commission also suggested Polish secret police, the Służba Bezpieczeństwa, involvement in these crimes.