Karl Josef Silberbauer (21 June 1911 – 2 September 1972) was an Austrian police officer, Schutzstaffel (SS) member, and undercover investigator for the West German Bundesnachrichtendienst (federal intelligence service).

He was then assigned to Amsterdam and attached to "Sektion IV B4", a unit recruited from Austrian and German police departments and which handled arrests of hidden Jews throughout the occupied Netherlands.

On 4 August 1944, Silberbauer was ordered by his superior, SS-Obersturmführer (Lieutenant) Julius Dettmann,[4] to investigate a tip-off that Jews were being hidden in the upstairs rooms at 263 Prinsengracht.

[9] After his release, Silberbauer was recruited by the West German Federal Intelligence Service (BND), and spent ten years as a mole, or undercover operative.

According to Der Spiegel reporter Peter-Ferdinand Koch, who learned of his postwar activities while researching BND employment of former Nazis, Silberbauer infiltrated neo-Nazi and pro-Soviet organizations in West Germany and Austria.

[10][11] Possibly due to BND pressure, Silberbauer was reinstated by the Viennese Kriminalpolizei (Kripo) in 1954, four years after the German publication of Anne Frank's diary, and promoted to the rank of Inspektor.

The Dutch police detectives who had assisted with the raid were identified by Miep Gies, who recalled their commander as having a working-class Vienna accent.

In late spring 1963, after ruling out numerous Austrians with similar names, Wiesenthal was loaned a wartime Gestapo telephone book by Dutch investigators.

[14] Upon his arrival in Vienna, Wiesenthal immediately telephoned Dr. Josef Wiesinger, who investigated Nazi crimes for the Austrian Ministry of the Interior.

Upon being told that Silberbauer might still be a policeman, Wiesinger insisted that there were "at least six men on the Vienna police force" with the same surname and demanded a written request.

After Izvestia praised "the detective work of the Austrian comrades", an infuriated Wiesenthal leaked Silberbauer's address to the Dutch media.

As Dettmann had committed suicide in prison (Huis van Bewaring, Havenstraat 6, Amsterdam, the Netherlands) on 25 July 1945, the second investigation also hit a dead end.