 During this period, he began attending university events, including lectures organized by left-wing revolutionary students by Theodor W. Adorno, Jürgen Habermas and Oskar Negt.He studied the works of Marx, Mao and Hegel and became a member of the militant group, "Revolutionärer Kampf" (Revolutionary Struggle).Fischer was a leader in several street battles involving the radical "Putzgruppe" (literally "cleaning squad", with the first syllable being an acronym for "Proletarische Union für Terror und Zerstörung", "Proletarian Union for Terror and Destruction"), which attacked a number of police officers.