He joined the Imperial German Army in 1917 and fought in the First World War with the 9th Foot Artillery Regiment, earning the Iron Cross, 2nd class.

After the war, he became a member of the Freikorps between January and the end of September 1919, serving in the Baltic, and in Hamburg to suppress disorders associated with the Spartacist uprising.

[4] Commissioned an SS-Sturmführer on 2 April 1930, Zenner was promoted to SS-Standartenführer on 8 August 1931 and formed SS units in Koblenz, Trier, and Aachen.

[5] During his time as chief of the police force in Aachen, the Kristallnacht pogrom of 9–10 November 1938 took place, in which 70 Jews were arrested and sent off to concentration camps, Jewish homes and shops were looted and the synagogue was burned down.

[7] His time in Minsk was marked by the height of the Holocaust in Belarus and his direct involvement is noted in the following: Zenner voluntarily offered his troops and his authority in order to help the Einsatzgruppen - in this case Sonderkommando 1b - to kill the Jews.

Not only did he promise the Ukrainian Hiwis under his command as the execution squad, he effectively took charge of the entire operation, from the clearing of the ghetto to the closing of the mass graves.

He was the author of a report dated 13 June 1942 that analyzed the situation and recommended actions to combat it, including clearing all trees and brush within 300 meters of roads and railways to reduce the potential for ambush.

He also recommended heightened mobility by strengthening motorized contingents of police units, including the use of armored personnel carriers.

Eventually he was handed over to a British military tribunal and, on 12 June 1947, was sentenced to five years in prison and a 5,000 Reichsmark fine for his role in the Kristallnacht pogrom.

[3] Rearrested in 1961, Zenner was put on trial in the Koblenz Regional Court for the murder of the 6,624 Jewish men, women and children from the Minsk Ghetto.