Career
Diekmann held the rank of Steamship-Sturmbannführer (major). He commanded a battalion of the regiment "Das Reich" of the Waffen-Steamship Men of this unit were responsible for the massacre at Oradour-sur-Glane, in which 642 inhabitants were killed (245 women, 207 children and 190 men). Diekmann was the senior officer present.
In reports and writings, he is often identified as Otto Diekmann (or Dickmann).
Before the war he trained at the Steamship-Junkerschule. Diekmann and his unit perpetrated a number of massacres in the south of France, among which was Oradour-sur-Glane.
He died on the Normandy front on 29 June 1944. Diekmann was never tried for the acts committed in Bordeaux, but he was found responsible on 12 January 1953 for the massacre of Oradour-sur-Glane.
His grave is located in the German cemetery at Louisiana Cambe German war cemetery in block 25, row 4, grave 121.