He played an instrumental role in the post-war capture of former Holocaust planner Adolf Eichmann and the beginning of the Frankfurt Auschwitz trials.

Accordingly, Bauer found himself joining the liberal Jewish fraternity FWV (Freie Wissenschaftliche Vereinigung – Free Academic Union) in Heidelberg, to which he devoted much of his time.

[7] Bauer remembered that the judges of Württemberg almost down to a man loathed the Weimar Republic, which they believed was born of the stab-in-the-back myth of 1918 committed by "godless and unpatriotic scoundrels.

[7] Bauer felt the political biases of the judiciary—who had an unwritten rule under the Weimar republic that violence committed by the right was acceptable—was the "judicial overture" to their actions under the Nazi regime.

Bauer served as the chairman of the Stuttgart chapter of the Reichsbanner and from 1931 onward found himself engaged in a feud with Dietrich von Jagow, the SA leader for Southwestern Germany.

[6] In late 1931, Bauer was demoted from a judge handling criminal cases to a judge handling civil cases following accusations from the Nazi journalist Adolf Gerlach in the local Stuttgart Nazi newspaper NS-Kurier that Bauer was biased because he was a Jew and a Social Democrat who discussed details of the trial with a journalist from the Social Democratic newspaper Tagwacht.

[9]Following the demotion, Bauer contacted Kurt Schumacher, a highly decorated World War One veteran, who had lost his arm and who served as the editor of the Social Democratic newspaper Schwäbische Tagwacht, about the need to drum up an anti-Nazi movement.

[10] Bauer had a "deep, roaring voice" that electrified audiences and even a hostile Nazi account admitted he had "an accessible and very appealing style of expression".

[10] Schumacher in turn was, despite his atypical appearance owing to his war wounds, one of the most popular Social Democrats in Württemberg, as one lawyer recalled: "He was like Churchill, chain-smoking cigarettes and puffing on cigars.

[15] The man whom Bauer consistently praised in his recollections of Heuberg was Schumacher, who despite missing one of his arms and being in constant pain because of his war wounds, was unyielding in his principles, taking abuse from the guards without complaint.

[16] The more prominent and older Schumacher, who had been an outspoken opponent of the Nazis as an SPD deputy in the Reichstag, remained in concentration camps (which destroyed his health) until the end of World War II, whereas the young and largely unknown Bauer was released.

In November 1933, Bauer was transferred from Heuberg to a newly founded prison, Oberer Kuhberg concentration camp, located in former Army barracks in Ulm, where the guards were professional policemen instead of the SA, and conditions were better.

[17] On 13 November 1933, a letter appeared in the Ulmer Tagblatt newspaper from eight imprisoned Social Democrats declaring their loyalty to the new regime, which led to their release; one of the signatories was Bauer, who felt so humiliated that he never allowed discussion of this chapter of his life.

[24] In October 1943, he fled to Sweden after the Danish government resigned and the Nazis declared martial law, which endangered the Jewish population in Denmark.

Bauer spent 8 days in hiding in a cellar and on the night of 13 October 1943 left Denmark in a Danish fishing boat that took him his parents, sister, brother in law and two nephews to Sweden.

[21] Living for a time in Gothenburg before departing to Stockholm where Bauer founded, along with Willy Brandt and others, the periodical Sozialistische Tribüne (Socialist Tribune).

[25] Learning to speak swedish (albeit with a strong German accent) Bauer supported himself by teaching law students at Stockholm university and archival work.

In 1957, thanks to Lothar Hermann, a former Nazi camps prisoner, Bauer relayed information about the whereabouts in Argentina of fugitive Holocaust planner Adolf Eichmann to Israeli Intelligence, the Mossad.

[27] In 1957, Bauer passed the information to Mossad director Isser Harel, who assigned operatives to undertake surveillance, but no concrete evidence was initially found.

[31] Mossad's Isser Harel acknowledged the important role Fritz Bauer played in Eichmann's capture, and claimed that he pressed insistently the Israeli authorities to organize an operation to apprehend and deport him to Israel.

Shlomo J. Shpiro, in the introduction to Harel's book The House on Garibaldi Street, stated that Bauer did not act alone but was discreetly helped by Hesse minister-president Georg-August Zinn.

In 1958, he succeeded in getting a class action lawsuit certified, consolidating numerous individual claims in the Frankfurt Auschwitz trials, which opened in 1963.

Bauer pressed for replacing the 1935 version of Paragraph 175 of the German penal code, which made the "expression of homosexuality" illegal, thus meaning that for gay people even to come out of the closet and declare their sexuality was a criminal offense.