During the Second World War, in the early part of 1940, he married the well-known poet Zuzanna Ginczanka in Lwów, then newly occupied by the Soviet Union, where both sought shelter from the Germans. Following Nazi Germany's attack on the Soviet Union of 22 June 1941 and the Nazi occupation of Lwów later the same month, he moved with his wife to Kraków in September 1942, where he disguised his identity by assuming the pseudonym Michał Danilewicz. However, he was eventually arrested by the Gestapo early in 1944, and subsequently perished at their hands. On 6 April 1944 there appeared pasted on the walls of Kraków an announcement issued by the "Summary Court-martial of the Security Police" ("Standgericht der Sicherheitspolizei") listing 112 names of people sentenced to death: the first 33 names were those on whom the sentence of death had "already" been carried out, the rest were those awaiting execution. Michał Weinzieher's name is among the latter. Although the precise date of his death is uncertain, it is known that he had predeceased his wife, who was also murdered by the Nazis several months later.