The son of an Imperial German Navy officer, Koch was born in Benevento. Koch served as a lieutenant in the Grenadiers where he was unpopular with his fellow soldiers and was dismissed from the army in 1939 for insulting a superior officer. Recalled on the eve of the war, he saw continuous service until the armistice of September 1943, after which he moved to Florence.
Settling in the Social Republic in the north of Italy, Koch joined the 'Special Service of Republican Police' led by Tullio Tamburini. It was in January 1944 that he established Banda Koch as a special task force charged with hunting down partisans and rounding up deportees for the Germans. Koch came under the protection of 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. 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.
Feared 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. He soon fell into Allied hands and was convicted of six charges at the High Court. He was executed at Rome's Forte Bravetta aged 26.