After the occupation of France, Kieffer went to Paris on behalf of the RSHA to conduct counter-espionage activities against the French Resistance and the Allies' SOE. His commanding officer was Sturmbannführer Karl Bömelburg, head of the Gestapo in occupied France. Kieffer was based at 84 Avenue Foch, the headquarters of the Sicherheitsdienst in Paris. From here he directed operations to capture Allied agents, escaped POWs and resistance fighters. He was credited as an expert in radio detection procedures. He also used his police training to turn French and British spies into double agents for the German counter-intelligence operation known as Funkspiel. In 1942, after he had been promoted to Sturmbannführer, he began working with Klaus Barbie, who had become head of the Sicherheitsdienst in Lyon. Kieffer assisted in the capture of French resistance leader Jean Moulin. Although he did not speak French or English, and always used an interpreter to speak to prisoners, Kieffer personally interrogated Moulin at his headquarters in Paris. On or around 13 October 1943, British agent Noor Inayat Khan was arrested and interrogated at 84 Avenue Foch by Kieffer. During that time, she attempted escape twice. He later testified to Vera Atkins from SOE after the war that Khan did not give him a single piece of information but lied consistently. When Atkins began to describe the death of Khan at Dachau concentration camp, Kieffer started to cry. To which Atkins replied, "Kieffer, if one of us is going to cry it is going to be me. You will please stop this comedy."
POW killings
In July 1944, Kieffer was in command of the SS troops who executed captured SAS men taking part in Operation Bulbasket. Informants had told the SD the SAS camp was located in a forest near Verrières, Vienne. The 17th SS Panzergrenadier Division Götz von Berlichingen attacked the camp at dawn. As the Germans searched the forest, 34 SAS men and some French Resistance fighters who were trying to break out were ambushed and captured. The SAS leader, 24-year-old Lieutenant Tomos Stephens, 24, from Llansteffan, Carmarthenshire, was beaten to death by an SS officer using a rifle butt; some of the French fighters were summarily shot. In 2019, on the 75th anniversary of the killing of Lt Stephens, he along with the other victims were commemorated at a remembrance ceremony near Verrieres. Five days later the 30 surviving SAS men were taken by Kieffer to woods near Saint-Sauvant, Vienne where they were forced to dig their own graves. Kieffer then had the men shot. Their bodies were then buried. After the war, the victims were re-interred in the village cemetery of Rom, Deux-Sèvres.
Trial and execution
In 1945, Kieffer was captured by British troops. He was put on trial for war crimes at Wuppertal in the British Occupation Zone. The trial was told that Kieffer had removed the uniforms of the SAS men and had the bodies dressed in civilian clothes and buried in a mass grave together with Sten Guns to make it look like they had died as a result of a mistaken shoot-out with local Resistance members. One of Kieffer's interpreters from 84 Avenue Foch testified at his trial, they said, "Kieffer was not cruel" and they had "seen him stop a guard from hitting a prisoner". The man said Kieffer did not want "maltreatment" he only "wanted information". However, the interpreter testified to Kieffer's darker side. He said that he made a deal with Francis Suttill to trade information about the locations of other agents and supplies in exchange for a guarantee that those agents would be allowed to live. But instead they were all killed. Kieffer was found guilty and sentenced to death by hanging. He was executed on the gallows at Hamelin prison by British executioner Albert Pierrepoint on 26 June 1947.
