The purchase of the diaries continued, and by June 1982 Gruner + Jahr possessed 35 volumes. In early 1983 the company took the decision to work towards a publication date for the diaries. To ensure wide readership and to maximise their returns, "Stern" issued a prospectus to potentially interested parties, "Newsweek", "Time", "Paris Match" and a syndicate of papers owned by Murdoch. "Stern" rented a large vault in a Swiss bank. They filled the space with Nazi memorabilia and displayed various letters and manuscripts. The first historian to examine the diaries was Hugh Trevor-Roper, who was cautious, but impressed with the volume of documentation in front of him. As the background to the acquisition was explained to him he became less doubtful; he was falsely informed that the paper had been chemically tested and been shown to be pre-war, and he was told that "Stern" knew the identity of the officer who had rescued the documents from the plane and had stored them ever since. By the end of the meeting he was convinced that the diaries were genuine, and later said "who, I asked myself, would forge sixty volumes when six would have served his purpose?" In an article in "The Times" on 23 April 1983 he wrote:  I am now satisfied that the documents are authentic; that the history of their wanderings since 1945 is true; and that the standard accounts of Hitler's writing habits, of his personality, and even, perhaps, of some public events may, in consequence, have to be revised. The day after Trevor-Roper gave his opinion of authenticity, Rupert Murdoch and his negotiation team arrived in Zürich. A deal was provisionally agreed for $2.5 million for the US serialisation rights, with an additional $750,000 for British and Commonwealth rights. While the discussions between Murdoch and Sorge were taking place, the diaries were examined by Broyle and his "Newsweek" team. After lengthy negotiation Broyle was informed that the minimum price "Stern" would consider was $3 million; the Americans returned home, informing Hensmann that they would contact him by phone in two days. When Broyle contacted the Germans he offered the amount, subject to authentication by their chosen expert, Gerhard Weinberg. In 1952 Weinberg, a cautious and careful historian, had written the "Guide to Captured German Documents", for use by the US military; the work is described by Hamilton as definitive in its scope of the subject.