The Knight's Cross (German: Ritterkreuz), and its variants were the highest awards in the military and paramilitary forces of Nazi Germany during World War II.

[1] After the Landespolizei (state police) was transferred into the Wehrmacht, Riedel, holding the rank of Polizei-Oberwachtmeister, joined the Army and was posted to the 1st company of Infantry-Regiment 84 of the 8th Infantry Division.

The division had been raised from troops of the Landwehr (national militia) in Oppeln, present-day Opole in Poland, and was under the command of Generalmajor (Major General) Ferdinand Neuling.

[2] One month later, on 28 January, Riedel, who had been injured by artillery shell splinter on his left side, was taken prisoner of war by Soviet forces at the field hospital of the 71st Infantry Division during the Battle of Stalingrad.

[5][Note 2] End-December 1954, Riedel was recruited by Oberstleutnant (Lieutenant Colonel) Rudolf Israel, a representative of the Ministerium für Staatssicherheit (MfS—Stasi), with the intention to have a secret informant among the divisional commanders of the NVA.

[7] Riedel was then transferred to the Institut für Deutsche Militärgeschichte (IDMG—Institute for German Military History) based in Potsdam, taking the position of deputy leader.