He volunteered to fight in the Spanish Civil War in 1936. Studied in Berlin, Germany from 1939 to 1941, and spoke fluent German. Volunteered to fight on the Russian front in 1941, but was injured by frostbite. His experiences in war turned him against Fascism, and he refused to swear allegiance to the Italian Social Republic government in 1943. For this, he was deported to Innsbruck, Austria on 9 September 1943, but managed to return to Milan, Italy on 20 October 1943. There he founded an underground newspaper that promoted Christianity and Christian alteratives to Facism. Due to acts like the deportation of Jews, Teresio gave up all thoughts of reconciliation with Facism, and began fighting in the Italian Resistance. Arrested on 27 April 1944 in Milan, he was imprisoned in a series of prisons, and routinely tortured by the Nazis, he was known for sharing his meagre rations with other prisoners, and treating their injuries. At one point he was imprisoned with and befriended Blessed Odoardo Focherini. He was beaten to death for trying to defend a Ukranian prisoner and cremated at the Hersbruck camp and his ashes dumped in a common grave.
Posthumously awarded the Medal of Military Valor.
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