To demonstrate that forgery by typewriter was not merely a theoretical possibility but had actually occurred in the Hiss case, the defense sought to show that Exhibit #UUU was not Hiss's old machine but a newer one altered to type like it. According to former Woodstock executives, the production date of a machine could be inferred from the machine's serial number. The serial number on the Exhibit #UUU typewriter indicated that it would have been "manufactured" after the man who sold the Hiss machine had retired from the company and the salesman insisted that he did not sell any typewriters after his retirement. Decades later, when FBI files were disclosed under the Freedom of Information Act, it turned out that the FBI had also doubted that the trial exhibit was Hiss's machine and for exactly the same reasons; although the FBI expressed these concerns internally as the first trial was about to begin, the public did not learn about the FBI's doubts until the mid-1970s.