"Who hired the white horse and buggy--if it was hired--that Frank Scanlan saw standing outside of the Windsor Theatre building on that memorable May night?" These were the questions to which the friends of the murdered physician now directed themselves. The body had been found; the cottage in which the crime had been committed--with all its mute but gory testimony--had been located. But even now the wheels of the mill of justice had scarce begun to revolve. Dr. Cronin had left his home alive; he had reached the cottage alive. Whose rig was it that took him to it? The question that was uppermost in the minds of thousands of people was soon to be answered--answered, too, in a manner that furnished a still more startling episode to the already startling tragedy. For the man that hired the horse and vehicle that carried the Irish Nationalist to his doom was a trusted officer in the employ of the city of Chicago; a man who, from the day of the disappearance, had, enjoying the full confidence of his superiors, been apparently working with might and main to bring about a solution of the mystery. It was Daniel Coughlin, detective. COUGHLIN HIRES THE RIG. Coughlin was attached to the East Chicago Avenue Police Station, which at that time was under the direction of Captain Michael J. Schaack, who had gained an international reputation for his brilliant work in connection with the celebrated Anarchist cases. The station house was located within a few doors of the southwest corner of Clark Street and Chicago Avenue. Little more than half a block north, on the former street, was a livery stable kept by Patrick Dinan. Naturally enough, as a result of his close proximity to the station, Dinan knew about all the officers and they knew him. Moreover, if any of them wanted a rig at any time to take their family or friends for a drive, they almost invariably went to No. 260 North Clark street to get it. So far as Dinan was concerned, therefore, there was nothing remarkable in the fact when, early on the morning of the day that the physician disappeared, Coughlin called at the stable. [Illustration: DANIEL COUGHLIN, DETECTIVE.] "I want you to keep a rig in readiness for a friend of mine to-night," he said, "and I don't want you to say a word about it. When he calls for it give it to him, and I'll be responsible for it." "All right," was Dinan's response. "I will have one on hand." The liveryman said afterward that he did not pay much attention to the remark that he was to "keep still about it," from the fact that Coughlin was often in the habit of hiring cabs and rigs to do detective work. In fact, he did not pay any attention to it at all, as there was nothing out of the common in his manner or conversation. [Illustration: LIVERYMAN DINAN'S STABLE WHERE THE WHITE HORSE AND BUGGY WERE HIRED.] [Illustration: THE WHITE HORSE AND BUGGY.]