As is inevitably the nature of the extensive Nazi persecution, the exact number of all the victims in Germany and Nazi-occupied countries cannot be known. At this point Jehovah's Witnesses have documented in their archives the names of over 12,000 persecuted Witnesses and have found that among the masses of humanity who passed through the gates of Nazi prisons and concentration camps were over 10,000 Jehovah's Witnesses. Of the total number, over 1,400 deaths have been documented, including more than 350 males and females who were executed.
http://www.chgs.umn.edu/museum/responses/steyer/jWitnesses.html