Who Was the Russian Angel?

I have been trying to find out who the Russian Angel was. One of my clients, who is now dead, worked for the secret service during the second world war and I am writing a book about his Court Martial. His name was Frank Edmunds and he was an interrogator at Bad Nenndorf. I have found that he was responsible for discovering or uncovering  “the Russion Angel in around 1945, but I cannot find out what the Russian Angel was and did and why the Russian Angel had to be discovered. Can anyone help?