The KPD was banned in the 1950s by the revanchist West German state. At the same time they gave jobs to old Nazis and encouraged neo nazism.
A dodgy deal was struck to legalise the party in the 1960s but it was not allowed to use the name KPD but instead the DKP and had to have a revisonist BRS type parliamentary road programme.
Not surprisingly many anti-revisionist and Maoist groups flourished in west Germany along with the Baader Meinhof group