On 6 August 2004, fifteen years after the Wall came down, Lorenz, then aged 73, was one of two senior party officials found guilty by the Berlin regional court as accessories to murder.

The case involved Michael Bittner, Lutz Schmidt and Chris Gueffroy, three citizens of the former German Democratic Republic who had been shot dead while trying to escape to West Berlin.

He joined the SPD (Social Democratic Party of Germany/Sozialdemokratische Partei Deutschlands) in 1945 and the FDJ (Free German Youth/Freie Deutsche Jugend) in 1946.

In 1947 he attended the Economics School at Annaberg, moving on for 1948/49 to the ABF (literally "Workers and Farmers Faculty" / "Arbeiter-und-Bauern-Fakultät") at Chemnitz and Leipzig universities.

Away from Berlin, between March 1976 and November 1989 Siegfried Lorenz was First Secretary of the SED regional leadership for Chemnitz in the south of the country.