He served as head of German police and security services (Sicherheitspolizei and SD) in Rome during the Second World War and was responsible for the Ardeatine massacre.

[3] Kappler was posted to Rome as head of the Sicherheitsdienst (SD) and, from the beginning of the Second World War, he cooperated closely with the Italian police.

[1][4][5][6][7] Kappler was immediately put in charge of implementing the Holocaust in Italy in both Rome and Lazio;[4] in his first action, 1,023 Roman Jews were rounded up and deported to Auschwitz; where only 16 survived.

The Monsignor's activities covertly assisting Jews and other fugitives led both Kappler and his Italian colleague Pietro Koch to repeatedly, and vainly, plot O'Flaherty's kidnapping, torture, and summary execution.

During those same years, Kurtna covertly spied for the Soviet Union, with devastating results for the many underground priests and faithful whose names he passed to the NKVD.

Kurtna, however, turned the tables on Kappler by stealing the top-secret Sicherheitsdienst codebooks from his office during the chaos that surrounded the Liberation of Rome.

Kappler's second-in-command in Rome, SS-Captain Erich Priebke, managed to escape to Argentina and was not extradited to Italy to face trial over his own role in the Ardeatine Caves Massacre until 1996.

On a visit in August 1977, she carried him out in a large suitcase (Kappler weighed about 47 kg (104 lb) at the time) and escaped to West Germany, assisted by apparently unwitting Carabinieri member.

[3][9] Despite demands that Kappler be returned to Italy, the West German authorities refused to extradite him and did not prosecute him for any further war crimes, reportedly owing to his ill-health.