As my eye fell on that figure, a cold thrill ran through me.  For a moment I only knew something important had happened.  Next instant I realised what the thrill portended.  I could only see the man’s back, to be sure, but I knew him in a second.  I had no doubt as to who it was.  This was him—­the murderer!

Yes, yes!  There could be no mistaking that arched round back that had haunted me so long in my waking dreams.  I knew him at sight.  It was the man I had seen on the night of the murder getting out of the window!

Perhaps I was overwrought.  Perhaps my fancy ran away with me.  But I didn’t doubt for a second.  I rose from my seat, and in a tremulous voice called Jane into the room.  Without one word I laid both pictures down before her together.  Jane glanced first at the one, then turned quickly to the other.  A sharp little cry broke from her lips all unbidden.  She saw it as fast and as instinctively as I had done.

“That’s him!” she exclaimed, aghast, and as pale as a sheet.  “That’s him, right enough, Miss Una.  That’s the very same back!  That’s the very same hand!  That’s the man!  That’s the murderer!”

And indeed, this unanimity was sufficiently startling.  For nothing could have been more different than the dress in the two cases.  In the murder scene, the man seemed to wear a tweed suit and knickerbockers,—­he was indistinct, as I said before, against the blurred light of the window:  while in the athletic scene, he wore just a thin jersey and running-drawers, cut short at the knee, with his arms and legs bare, and his muscles contracted.  Yet for all that, we both knew him for the same man at once.  That stooping back was unmistakable; that position of the hand was characteristic and unique.  We were sure he was the same man.  I trembled with agitation.  I had a clue to the murderer!

Yet, strange to say, that wasn’t the first thought that occurred to my mind.  In the relief of the moment, I looked up into Jane’s eyes, and exclaimed with a sigh of profound relief: 

“Then you see how mistaken you were about the hands and Aunt Emma!”

Jane looked close at the hand in the photograph once more.

“Well, it’s curious,” she said, slowly.  “That’s a man, sure enough:  but he’d ought to be a Moore.  The palm’s your aunt’s as clear as ever you could paint it!”

I glanced over her shoulder.  She was perfectly right.  It was a man beyond all doubt, the figure on the wagon.  Yet the hand was Aunt Emma’s, every line and every stroke of it; except, of course, the scars.  Those, I saw at a glance, were wholly wanting.

And now I had really a clue to the murderer.

Yet how slight a clue!  Just a photograph of men’s backs.  What men?  When and where?  It was an athletic meeting.  Of what club or society?  That was the next question now I had to answer.  Instinctively I made up my mind to answer it myself, without giving any notice to the police of my discovery.