That concluded Garrick’s investigation, and, after thanking the coroner, who had gone out of his way to accommodate us, we started back to town.

“Well,” I remarked, as we settled ourselves for the tedious ride into the city in the suburban train, “we don’t seem to have added much to the sum of human knowledge by this trip.”

“Oh, yes, we have,” he returned, almost cheerfully, patting the black camera which he had folded and slipped into his pocket.  “We’ll just preserve the records which I have here.  Did you notice what it was that I photographed?”

“I saw something,” I replied, “but I couldn’t tell you what it was.”

“Well,” he explained slowly as I opened my eyes wide in amazement at the minuteness of his researches, “those were the marks of the tire of an automobile that had been run up into the bushes from the road.  You know every automobile tire leaves its own distinctive mark, its thumb print, as it were.  When I have developed my films, you will see that the marks that have been left there are precisely like those left by the make of tires used on Warrington’s car, according to the advertisement sent out by McBirney.  Of course, that mere fact alone doesn’t prove anything.  Many cars may use that make of tires.  Still, it is an interesting coincidence, and if the make had been different I should not feel half so encouraged about going ahead with this clew.  We can’t say anything definite, however, until I can compare the actual marks made by the tires on the stolen car with these marks which I have photographed and preserved.”

If any one other than Garrick had conceived such a notion as the “thumb print” of an automobile tire, I might possibly have ventured to doubt it.  As it was it gave food enough for thought to last the remainder of the journey back to town.

CHAPTER IV

THE LIQUID BULLET

On our return to the city, I was not surprised after our conversation over in New Jersey to find that Garrick had decided on visiting police headquarters.  It was, of course, Commissioner Dillon, one of the deputies, whom he wanted to see.  I had met Dillon myself some time before in connection with my study of the finger print system, and consequently needed no second introduction.

In his office on the second floor, the Commissioner greeted us cordially in his bluff and honest voice which both of us came to know and like so well later.  Garrick had met him often and the cordiality of their relations was well testified to by Dillon’s greeting.

“I thought you’d be here before long,” he beamed on Garrick, as he led us into an inner sanctum.  “Did you read in the papers this morning about that murder of a girl whose body was found up in New Jersey in the underbrush?”

“Not only that, but I’ve picked up a few things that your man overlooked,” confided Garrick.

Dillon looked at him sharply for a moment.  “Say,” he said frankly, “that’s one of the things I like about you, Garrick.  You’re on the job.  Also, you’re on the square.  You don’t go gumshoeing it around behind a fellow’s back, and talking the same way.  You play fair.  Now, look here.  Haven’t I always played fair with you, Garrick?”