After the outbreak of the Polish Defensive War of 1939 he was one of the co-founders of the "Civilian Committee of the Defence of Lwów" that organized the defensive measures for the city during the siege of that city. After the city surrendered to the Soviets and was annexed by the USSR he was relieved of his office, but remained one of the professors of the University. After the outbreak of the Russo-German War in 1941, on July 4 he was arrested by the Nazis and murdered in what became known as the massacre of Lwów professors. Among the victims were also three of his sons: Bronisław (b. 1916), Zygmunt (b. 1918) and Kazimierz (b. 1923).