Yet, I reflected, following Norton, in all this mass of material, the thief seemed to have selected one, apparently insignificant, dagger, the thing which Norton prized because, somehow, it bore on its blade something which he had not, as yet, been able to fathom.

Though Kennedy looked thoroughly and patiently, it seemed as though there was nothing there to tell any story of the robbery, and he turned his attention at last to other parts of the Museum.  As he made his way about slowly, I noted that he was looking particularly into corners, behind cabinets, around angles.  What he expected to find I could not even guess.

Further along and on the same side of the building we came to the section devoted to Egyptology.  Kennedy paused.  Standing there, upright against the wall, was a mummy case.  To me, even now, the thing had a creepy look.  Craig pushed aside the stone lid irreverently and gazed keenly into the uncanny depths of the stone sarcophagus.  An instant later he was down on his hands and knees, carefully examining the interior by means of a pocket lens.

“I think I have made a start,” he remarked, rising to his feet and facing us with an air of satisfaction.

We said nothing, and he pointed to some almost undiscernible marks in a thin layer of dust that had collected in the sarcophagus.

“If I’m not mistaken,” he went on, “your thief got into the Museum during the daytime, and, when no one was looking, hid here.  He must have stayed until the place was locked up at night.  Then he could rob at his leisure, only taking care to confine his operations to the time between the rather infrequent rounds of the night watchman.”

Kennedy bent down again.  “Look,” he indicated.  “There are the marks of shoes in the dust, shoes with nails in the heels, of course.  I shall have to compare the marks that I have found here with those I have collected, following out the method of the immortal Bertillon.  Every make of shoes has its own peculiarities, both in the number and the arrangement of the nails.  Offhand, however, I should say that these shoes were American-made—­though that, of course, does not necessarily mean that an American wore them.  I may even be able to determine which of a number of individual pairs of shoes made the marks.  I cannot tell that yet, until I study them.  Walter, I wish you’d go over to my laboratory.  In the second right-hand drawer of my desk you’ll find a package of paper.  I’d like to have it.”

“Don’t you think you ought to preserve the marks?” I heard Norton hint, as I left.  He had been watching Kennedy in open-eyed amazement and interest.

“Exactly what I am sending Walter to do,” he returned.  “I have some specially prepared paper that will take those dust marks up and give me a perfect replica.”

I hurried back as fast as I could, and Kennedy bent to the task of preserving the marks.

“Have you any idea who might have an object in stealing the dagger?” Kennedy asked, when he had finished.