On November 2, at Judge Thayer’s request, District Attorney Williams borrowed from Van Amburgh a plug gauge, a device for measuring the diameter of a gun barrel. He found Sacco’s pistol barrel to measure .3045 inches. Hamilton’s measurement had given the diameter as .2924 inches, but Williams thought little of the discrepancy since he himself had never seen a plug gauge before and felt he might easily have made a mistake. However, when Hamilton, on December 4, in the presence of the clerk of court, checked Sacco’s pistol with the gauge, he confirmed Williams’ measurement. Hamilton now observed that the fouled rusty barrel was shiny and, according to his later testimony in a special hearing before Judge Thayer, his first thought was that the court had been cleaning it. “I could not conceive in my mind why you would do it,” he told Thayer, “but I said to myself no one else could have done it.... I immediately dispelled it because I said, no court would alter an exhibit.” Whatever Hamilton’s opinion of the altered condition of the barrel and the variations in his first and second measurements, he afterward maintained that when he examined Sacco’s automatic on December 4 it never occurred to him that the barrel was anything but the original. Acting on Thompson’s request to make fresh firing tests, Judge Thayer on February 11 called in Van Amburgh to inspect Sacco’s Colt and determine its condition. With the district attorney present, Van Amburgh took the gun from the clerk of court and prepared to disassemble it. No sooner had he drawn back the slide than he saw that the barrel was not the barrel he had last examined. It looked brand-new. There was even a film of cosmoline on it. “Someone has switched barrels,” he at once told Williams. The two hurried to Judge Thayer. Thayer, after listening to them, announced that he would hold an investigation. Two days later he began hearings in his chambers with only Moore, Williams, Hamilton, Van Amburgh, and a stenographer present. Press and public were barred, unaware even that such hearings were taking place. They lasted just over three weeks. At the opening Clerk Worthington brought in the three pistols. The briefest examination made it clear to everyone that Sacco’s Colt had acquired a new barrel. Hamilton, not at all abashed that every finger seemed to point to him, admitted that the new barrel must have come from one of his pistols, but insisted that he had not made the switch. In his opinion this had been done by someone connected with the prosecution. After examining the fouled barrel in one of his own new guns under a microscope, Hamilton stated that he was unqualifiedly of the opinion it was not the Sacco barrel.