In the same year, Seidel began studying at the "Rudolf Diesel" engineering school [de] in Meißen.

While visiting Potsdam, the mayor of Bonn, Hans Daniels, made critical remarks about the East German government on live television.

After being dismissed from his post as mayor of Potsdam in 1989, Seidel was employed as a regional chairman of Workers and Farmers Inspection (Arbeiter-und-Bauern-Inspektionde [de]), an economic planning institution.

During the vote tabulation process, discrepancies in the results were reported to East German authorities by election scrutineers.

[4] The Socialist Unity Party (SED) then appointed Manfred Bille to succeed Seidel as mayor of Potsdam.

Seidel was arrested by the East German Volkspolizei in June 1990, together with his deputy Marlies Nopens and former city councillor Lothar Holz.

Seidel and his co-defendants received support from the conservative politician Lothar de Maizière, who called for amnesty.