Karl Hass, born October 5, 1912 in Kiel, Germany – died April 21, 2004 in Geneva, Switzerland, was SS officer and spy who was convicted of mass murder for his participation in one of Italy's worst massacres of World War II.

In 1934, Karl Hass joined the Sicherheitsdienst, the Nazi Party's intelligence service where his ruthlessness earned him the respect of his senior officers. After the downfall of Benito Mussolini, and the occupation of Italy by the Germans, Karl Hass was sent to Rome to set up a network of radio operators and to organize saboteurs behind the invading Allied lines. While in Rome, under SS-Obersturmbannfuhrer (Lieutenant-Colonel) Herbert Kappler, Karl Hass aided in the deportation of more than 1,000 Jews to Auschwitz concentration camp.

Karl Hass was also the officer who lured Princess Mafalda of Savoy, the daughter of King Victor Emanuel III of Italy, to his headquarters in Rome with claims that there was a message from her husband who was then being held in Berlin. On her arrival at the German command, Hass had the princess arrested and shipped to Germany where at Buchenwald concentration camp she was executed.

Following a March 23, 1944 bomb attack in the Via Rasella by Italian resistance fighters that killed 33 German soldiers, Karl Hass with Capt. Erich Priebke and his fellow officers rounded up 335 Italian men and young boys and the next day transported them to the Ardeatine caves at the outskirts of Rome. A cold, calculating killer, Hass, Priebke, and their soldiers systematically executed every one of them with a shot in the back of the head. The Ardeatine massacre is one of the most notorious in the Italian history of World War II.

After the War, SS-Hauptsturmfuhrer Karl Hass was captured by the Allies but rather than facing an International Military Tribunal for his war crimes, he was used by the United States Army Counter-intelligence Corps to spy on the Soviet Union. Only Herbert Kappler was ever charged with the Ardeatine cave massacre. In the early 1990s, Capt. Erich Priebke, who had helped Karl Hass with the executions, was found hiding in Argentina by an American television crew and eventually extradited to Italy to stand trial. In exchange for immunity, Karl Hass returned to Italy to testify against his fellow SS murderer. However, on the night before he was due to testify, Hass decided to remain loyal to his Nazi past and attempted to flee from his hotel room by climbing down from an outside balcony. He seriously injured himself after slipping and falling from the balcony and was taken to hospital where he ultimately gave testimony to Court officials. In the court records, Karl Hass admitted to executing two civilians but defended his actions by claiming he was only following orders.

His attempt to flee meant that Karl Hass lost his legal immunity from prosecution and he was finally brought to justice. Tried and convicted for his heinous crimes, in 1998 he was sentenced to life in prison. But, because of his advanced age and poor health, instead of a cellblock, Hass was held under limited house arrest in a retirement villa in his favorite area of Switzerland where he had resided for a number of years after the War. Given the freedom to leave for brief periods, Karl Hass spent his last years in the splendor of the beautiful Swiss Alps not far from his daughter who visited him regularly from her home in Geneva.