Franz was a cook and was not politically active before joining the SS in 1937, serving as a guard at Buchenwald. In 1939 he participated in various assignments regarding 'euthanasia' programs, during 1942 he was at Belzec and later Treblinka. He rose through the ranks as a guard. He afterwards was detailed to Italy. From 1945 to 1949 he worked as a laborer and from 1949 to 1959 he worked as a cook. He was arrested in 1959 and in 1965 was sentenced to life imprisonment. Franz's dog, Barry, was trained to assault prisoners at Treblinka and is said to have torn several to pieces—charges which Franz denied at his trial. The trail transcript indicates that Franz admitted to being in charge of Treblinka, but only after mass murder has stopped. He claimed his conscious was clear and he was innocent of any wrongdoing to any person.