"The assailant was clearly a tall, powerful man and left-handed. That was shown by the nature of the blow. That he had some knowledge of physiology is obvious from the fact that he made no attempt at a second blow to insure death, as a layman most likely would have done. He knew that he had smashed the occipital bone right into the brain. In his early years Sir Jasper studied medicine. "The crime committed, Sir Jasper proceeded to cover his tracks. With the poker he loosened the sockets of the bolts and that of the lock in order to give an impression that the door had been burst open from without. He then left the place and, to suggest robbery as a motive for the crime, he took with him the professor's gold watch, which he threw away. This was found a few hours later by the tramp whom you, Carfon, want to hang for a crime of which he knows nothing." There was a note of sternness in Malcolm Sage's voice. "But----" began the inspector. "I suspect," continued Malcolm Sage, "that after he had left the laboratory, Sir Jasper suddenly realised that the professor had probably recorded in his book all his processes. He returned, discovered the manuscript, and was for hours absorbed in it, at first smoking continuously, later too interested in his task to think of his pipe. It must be remembered that he had studied medicine." The inspector glanced across at Sir John Dene, who sat rigidly in his chair, his eyes fixed upon Malcolm Sage. "I rather think that he was aroused from his preoccupation by the ringing of the bell announcing the arrival of the professor's breakfast. He then realised that he could not leave the place until nightfall. He therefore ate that meal, carefully avoiding the marmalade, which he disliked, and subsequently he consumed the luncheon, and dinner, passed through the wicket." Malcolm Sage paused to press down the tobacco in his pipe. "He burned the manuscript, tearing up letters and throwing them into the waste-paper basket to give the appearance of Professor McMurray having had a clearing-up. He then destroyed all the test-tubes he could find. Finally he left the laboratory late on the Wednesday night, or early Thursday morning." "But how did you find out all this?" It was Sir John Dene who spoke. "First of all, Sir Jasper and the murderer smoke the same tobacco, 'Ormonde Mixture.' I verified that by picking Inspector Carfon's pocket." Taking a tobacco-pouch from a drawer Malcolm Sage handed it across the table. "You will remember Sir Jasper lent me his pouch. I had picked up some tobacco on the floor and on the hearth. "Secondly, the murderer was left-handed, and so is Sir Jasper. "Thirdly, the murderer does not eat marmalade and Sir Jasper had the same distaste." "But how----?" began the inspector.