He was apprehended in Paris on 30 September. He was released on bail and absconded to France on 10 July 1977. A campaign against his imprisonment was organized in which, in particular, Jean-Paul Sartre and Michel Foucault took part. Croissant was shown by Kurt Rebmann, then Attorney General of Germany, "to have organized his cabinet the operational reserve of West German terrorism".
dbr:Alternative_Liste_für_Demokratie_und_Umweltschutz.dbc:Party_of_Democratic_Socialism_(Germany)_politicians.dbr:Party_of_Democratic_Socialism_(Germany).wiki-commons:Special:FilePath/Klaus_Croissant_1977.jpg?width=300.
In 1992, his collaboration with the Stasi was made public. His girlfriend, the taz-publisher and green member of the European Parliament Brigitte Heinrich, was led by Croissant to join his work for the Stasi till her death in 1987. After his release, Croissant started to work for the Stasi, which registered him, in 1981, as Inoffizieller Mitarbeiter "IM Taler", Reg. He was sentenced to two-and-a-half years' imprisonment for supporting a designated terrorist organization. Lastly, the prospect which whole Europe passes under this type of control claimed by Germany. Conversely, the possibility that Croissant is delivered, returned to Germany where he risks the worst, or, simply expelled in a country of "choice" which would not accept him. In a platform published in Le Monde on 2 November 1977, Gilles Deleuze and Félix Guattari wrote: Three things worry us immediately: the possibility that many German men of the left in an organized system of denouncement, see their life becoming intolerable in Germany, and are forced to leave their country. He was extradited to West Germany the following day. He applied for political asylum but his plea was rejected by the court of criminal appeal of the Court of Appeal of Paris and an extradition order made on 16 November 1977 despite some protests in Germany, France and Italy. Er war später für die West-Berliner Alternative Liste und anschließend für die PDS politisch aktiv. Croissant wurde 1979 wegen Unterstützung einer terroristischen Vereinigung verurteilt. Er erlangte Bekanntheit als Verteidiger von Andreas Baader im Stammheim-Prozess gegen die Anführer der Rote Armee Fraktion. März 2002 in Berlin) war ein deutscher Strafverteidiger.