Hugh Trevor-Roper's investigation in autumn 1945 and his subsequent book have been reappraised by Geoffrey Parker and Sarah Douglas in The Journal of Military History. Parker questions whether a single person could have interrogated numerous witnesses single-handed and sifted their evidence in less than six weeks and suggests that Trevor-Roper spent most of his time reading the transcripts of interrogations carried out by others. Douglas writes that a collective effort of countless interrogators from all over Europe became "The Last Days of Hitler", a book the text of which she asserts remains the same through every edition. In fact extensive primary sources show that during his autumn enquiry Trevor-Roper personally questioned at least eighteen witnesses or persons with leads to witnesses, and in eleven of these cases a significant interrogation took place. Trevor-Roper was an exceptionally effective interrogator who elicited detail and meaning which had escaped previous questioners. His eagerness to question witnesses himself was not least due to recurrent problems with interrogations carried out by others. Indeed the majority of evidence in his book did not come from interrogations, but from pre-war books, wartime intelligence documents, eavesdropping material, diaries, memoirs, post-war publications, and documents originating from Hitler or the Doenitz government. Once published, the text of "The Last Days of Hitler" was changed significantly for later editions.
