After World War I and the dissolution of Austria-Hungary, the family left Austrian Silesia and settled in Garsten near Steyr, their ancestral home.

[2][3][4][5] As a result of the bankruptcy, Reder left his family and settled with an aunt in Vienna.

In December 1943, Reder was transferred to the newly formed 16th SS Panzergrenadier Division Reichsführer-SS and served in Italy until 1945.

He was tried by an Italian military court in Bologna for ordering the destruction of town of Marzabotto and other villages near Bologna in August and September of 1944 during so-called anti-partisan sweeps, and for ordering the execution of 2,700 Italian civilians in Tuscany and Emilia during the same period.

In October 1951, he was sentenced to life imprisonment at a fortress prison in Gaeta, on the Tyrrhenian Sea coast between Naples and Rome.

[9] Years later, a group of SS men whom Reder had commanded in 1944 were tried and convicted for their role in the Sant'Anna di Stazzema massacre.