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: 

========
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........
........

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