The son of an Imperial German Navy officer, Koch was born in Benevento.^[1] Koch served as a lieutenant in the Grenadiers where he was unpopular with his fellow soldiers and was dismissed from the Royal Italian Army in 1939 for insulting a superior officer.^[1] Recalled on the eve of the war, he saw continuous service until the armistice of September 1943, after which he moved to Florence.^[1]

Settling in the Social Republic in the north of Italy, Koch joined the Special Service of Republican Police led by Tullio Tamburini.^[1] In January 1944, he established the Banda Koch as a special task force charged with hunting down partisans and rounding up deportees, including Jews, for the Germans.^[1] Koch came under the protection of SS-Obersturmbannführer Herbert Kappler, SD chief in Koch's base of Rome, and as such had a free hand to employ whatever tactics he saw fit with Banda Koch, which soon became a by-word for cruelty and violence.^[1] Koch was given his own prisons and torture chambers and continued his activity in Florence and then Milan following the fall of Rome to the Allies.^[1] Along with police chief Pietro Caruso, who was independently involved in the killing of partisans, Koch was behind hundreds of deaths; the Social Republic government even ordered an amnesty for political prisoners not charged with murder out of fear that Koch would have them killed.^[2]

Disliked even by Benito Mussolini for his violent extremism, Il Duce eventually had his close ally Renzo Montagna arrest Koch for his excesses in October 1944.^[1] He soon fell into Allied hands, was tried by an Italian tribunal and was convicted of six charges at the High Court.^[1] He was executed at Rome's Forte Bravetta aged 26.^[1]