Thus the robbers would have had full opportunity to approach the safe unobserved and exercise their skill upon it, could they have secured entrance to the ticket-office. Nor was this a difficult matter, since the door leading into it was known to have three keys, in the hands of various employees of the road, from whom they might have been procured or stolen. More important still was the fact, ascertained by Mr. Bangs, that the safe itself had three keys, intrusted to as many men, whose duties required them to have access to the safe. It subsequently transpired that two of these keys had been made by the men who carried them, for their own convenience and without the knowledge of their superiors. The door leading into the ticket-office opened from the men's waiting-room, where people had been coming and going during the entire night of the robbery. Such of these people as could be found were questioned closely as to what they had observed on this night, but they could furnish no information that threw light upon the case. Some significance was found in the coincidence that nine years before there had been a robbery at Susquehanna, in which thirty thousand dollars had been stolen from the express company's safe. The Pinkertons knew that for years a band of professional thieves had been traveling through the country, operating on safes that could be opened with a key. Among them were experts in fitting locks, especially skilled in making keys from impressions, and known as professional "fitters." At first it was considered possible that the robbery had been committed by these men; but, after the most careful search and inquiry, Superintendent Bangs concluded that this was not the case and that the pouch had been stolen by some person or persons resident in Susquehanna, presumably by one or more of the railroad employees who had access to the office, or by persons intimately acquainted with some of the men who had keys to the safe. "Shadows" were put on all persons who might have had access to the ticket-office and the safe; but, although this was continued for weeks, nothing conclusive came to light.