From the book: 
The Lock and Key Library; Classic Mystery and Detective Stories 
Edited by Julian Hawthorne 

Published by The Review of Reviews Company - New York - 1909 

* The author of the pages that follow was chief special agent of the Secret Service of the United States Post-Office Department during pioneer and romantic days. The curious adventures related are partly from his own observation, and partly from the notebooks of fellow officers, operating in many sections of the Country. 

The stories are true, although, of course, justice demands that in some cases persons and places be usually disguised under fictitious names. 

The stories have interest not only for their exciting play of honest wits against dishonest, but also for the cautions they sound against believing things "too good to be true" from the pen of strangers. 

There is a class of post-office thieves who make a specialty of rifling the registered letters that pass through their hands in transit on journeys of greater or less length. Some of them have managed operations very shrewdly, in the evident belief that they had discovered an infallible method for doing the work and at the same time escaping detection. Too late they generally learn by sad experience that no patents can be taken out for the protection of crime. 

In this class of cases something tangible always remains to exhibit the peculiar style of workmanship belonging to each; and it would often surprise the uninitiated to learn how many traits of character, what indexes of habit and vocation, can be picked up by careful study of the minute points presented for inspection. Unless, however, an agent cultivates a taste for thoroughness even to details and trifles that might at first view appear utterly insignificant, he will never succeed in interpreting the hieroglyphics. 

At intervals of two or three weeks, beginning in the summer of 1871, registered packages passing to and fro from Chicago to a town in the interior of Dakota Territory, which for convenience will be called Wellington,--though that was not its name,--were reported to the department as rifled. As the season wore on, the complaints increased in frequency. Under the old method of doing business at headquarters, which often amounted practically to a distribution of the cases about equally "among the boys," the agent stationed at Chicago received most of them at first; then a part were sent to an agent in Iowa; and as the number multiplied, Furay, at Omaha, was favored with an occasional sprinkling. Under the present more perfect system, great care is taken to group together all the complaints growing out of each series of depredations, to locate the seat of trouble by comparisons carefully made in the department itself, and to give everything bearing on the subject to the officer specifically charged with the investigation. 

March came around before Mr. Furay found time to give personal attention to this particular thief. He then passed over the route to Wellington, eighty miles by stagecoach from the nearest railroad station, with ten intermediate offices. All the packages remained over night at Sioux City, Iowa, a fact sufficiently important to invite close scrutiny; but the detective soon became satisfied that he must look elsewhere for the robber. His suspicions were next directed to another office, where also the mails lay over night; but the postmaster bore a countenance so open and honest that he too was eliminated from the problem. 

He continued on to Wellington, skirmishing along the line, and observing the faces of the postmasters; but these studies in physiognomy threw no light on the mystery, as the officials of the department on the route, though far removed from central supervision, seemed to be all that their affectionate uncle at Washington could wish. On the return trip the detective was equally observant and equally perplexed. At that season the stage stopped for the night at Hannibal; but there, likewise, the postmaster shared the honest looks that seemed to prevail through eastern Dakota. 

Proceeding on, the passengers dined at Raven's Nest, where one Michael Mahoney, Sr., kept a small store and the post-office, running also--with the aid of a young son and a son-in-law--a farm. The store was managed by Michael Mahoney, Jr., a married son, who happened to be absent both when the special agent went up and when he returned. The face of the old man indicated that he was vicious, ignorant, and unscrupulous; but clearly he was not sharp enough to execute nice work like that under investigation. 

With the exception of a general knowledge of the offices, the special agent returned but little wiser for the trip, and concluded, as the best that could be done under the circumstances, to allow the bird to flutter a little longer before renewing the hunt. Meanwhile the thief grew more reckless, and the papers that came to Mr. Furay, though covering a fraction only of the depredations, located the thief on the lower end of the route, within fifty miles of the terminus. 

During the summer one or two other agents took up the matter cursorily, but made no discoveries. In the meantime Mr. Furay was kept too busily occupied with a succession of important cases in Nebraska to give much thought to the outlying territory of Dakota. At length, in September, he went carefully over the papers that had accumulated during his late prolonged absences, and soon knew exactly where to look for the chap who had so long plundered the public with impunity. 

For some time Chicago had been closing registered package envelopes with wax, which, on this route at least, effectually secured them against molestation. Imitating the example, Camden, Dakota, began to do the same; but, having no seal suitable for the purpose, improvised a substitute by using the flat surface of a rasp. 

Camden placed the wax near each end of the envelope, which materially interfered with the game of the thief, because it was just here that he operated. Evidently piqued that a rural postmaster should presume to outwit him, he studied hard to devise some means for opening these particular packages without leaving such traces of his handiwork as would attract the notice of other officials through whose hands they might subsequently pass. The effort was crowned with a measurable degree of success, for Mr. Furay, at the general overhauling referred to, was the first to discover that the seal had been tampered with. 

As it was necessary to break one of the seals, the object of the robber was to restore it as nearly as possible to its original appearance; and to effect this he used a dampened thimble, rolling it over the wax while the latter was hot. There was but one envelope of the kind in the lot, but it told the whole story to the eye that could penetrate its meaning. As the thimble passed along the edge, it left the mark of the rim, then a smooth, narrow band, followed by pointed elevations closely resembling continuous lines, thus: 

======== 
-------- 
........ 
........ 

On the opposite side of the same seal the wax flattened out so as to cover a good deal of surface; and, to give it the desired appearance, the manipulator resorted to the thimble again, but this time USED A DIFFERENT ONE, the indentations on the surface being perceptibly finer and more shallow. 

The violation of that single seal betrayed the thief, for the detective at once inferred that the job was done in a store where the operator had access to a variety of thimbles. Only one was required; and no person but a merchant would be likely to have more than one within convenient reach. In a store, however, it would be natural to take down a boxful, and place it on the counter, to be selected from at random. One is picked up, used, and thrown back. The operator now finds another spot that requires attention, and without waiting to hunt for the thimble that has already served as a seal,--for the wax is cooling and no time must be lost,--grasps the first that comes to hand, too absorbed in the main issue to give a thought to what would pass as an insignificant subsidiary trifle. No rascal is sharp enough to guard every point,--a general fact that illustrates over and over again, in the experience of man, the seminal truth that in a mercenary and physical as well as in a high and spiritual, sense there is neither wisdom nor profit outside of the limits of absolute integrity and unflinching uprightness. 

The detective laid aside the papers with a light heart, knowing that at last he was complete master of the situation. Below Camden on the infested route the post-office was kept in a store at two points only, and in one of those no thimbles were sold. The clew pointed unerringly to Raven's Nest as the spot where alone the requisite conditions to account for the imprint on the violated seal were to be found. Thither the officer accordingly went; and the moment his eye rested on Michael Mahoney, Jr., he recognized the heaven-branded features of a thief. 

Returning to Sioux City, he telegraphed to another agent, who had a large number of the cases growing out of the robberies, to come on at once. The two men took stations, one on each side of Raven's Nest, and in thirty hours they arrested the youthful criminal, who in the interval stole four decoy letters, and paid a portion of the contents to one of the officers who was testing him. 

Mr. Furay collected from the thief and his relatives the full amount stolen from the mails during the entire continuance of the depredations, restoring the money to the rightful owners dollar for dollar. Young Mahoney made a written confession, supplemented by three or four codicils relating to items which, to use his own language, "at first did not to me occur." He was tried the following February, and sentenced to the penitentiary for the term of three years. 

Within fifteen days from the time when the doors of the prison were closed upon the son, the villainous old father, acting perhaps on the theory that no two shots ever strike in exactly the same place, began also to rob the mails. In due time Mr. Furay again appeared on the scene and took the old reprobate away a prisoner. When the trial came on, a material witness for the prosecution happened to be absent, the lack of whose testimony proved fatal to the case, for after hanging a day and a night, the jury brought in a verdict of acquittal.

June 8, 1872, a law was approved making it a penal offense to use the mails for the purpose of defrauding others, whether residing within or outside of the United States. The postmaster-general was also authorized to forbid the payment of postal money orders to persons engaged in fraudulent lotteries, gift enterprises, and other schemes for swindling the public, and to instruct postmasters to return to the writers, with the word "fraudulent" written or stamped on the outside, all registered letters directed to such persons or firms. Prior to the enactment of this law, the most wholesale and barefaced operations were conducted by professional cheats, mainly through the facilities afforded by the mails, with almost absolute impunity. Letters addressed to bogus firms were indeed forwarded from the offices of delivery to the department as "fictitious" and "undeliverable," and many colluding postmasters were decapitated. Such petty measures of warfare served merely to annoy the vampires and to whet their diabolical ingenuity for the contrivance of new devices. Since the law of 1872 went into effect, however, the scoundrels have been compelled to travel a thorny road. Scores of arrests have been made, and in many cases the criminals have been sentenced to the penitentiary.