“The next morning Rodney Tait provided me with a time table of the first act. During rehearsal this morning I found that time table was correct, and I added to it the exact time the cue for murder was spoken by Hutchins. Then I saw you were the only actor on stage near enough Vladimir to stab him at the moment Hutchins spoke that line. Hutchins himself was the first to suspect that his own voice had been the signal for two murders. He wasn’t sure, so he tried to convey the information to me indirectly by a Shakespearean quotation. Even Pauline suspected you tonight when Inspector Foyle turned on the light in the lobby, and she saw that a curtain which looked black in a very faint light was really red. Of all colors, red is the first to lose its characteristic hue when light fails. Just as blood and lipstick look black in a dim light or a photograph, your red dressing gown looked black on the fire escape in the darkness beyond the faint red radiance from the Tilbury clock.”
“That is an ingenious reconstruction,” said Leonard. “But it’s largely surmise. You haven’t proved me guilty.”
“I haven’t, but the fly and the canary have.”
“What about the canary?”
“It was clever of you to steal Rodney’s surgical knives and break into Lazarus’ shop to sharpen them. That way you thought there would be no record that you had ever sharpened a knife or had one in your possession. But there was a record. First, the night before Ingelow’s murder you had a cut on your forefinger and Lazarus tells me such cuts are characteristic of knife-grinders whether professional or amateur. Secondly, each time you were in Lazarus’ shop you set the canary free. You even did so a third time this evening, when you broke into Milhau’s office to get another knife from his safe and saw that the canary’s cage was there. What sort of man would feel an irrational, irresistible impulse to set a caged bird free every time he saw one, regardless of consequences to himself or the bird? Only a man who knew how agonizing the sense of forced confinement can be—an ex-convict who had served a prison term that he considered unjust. You were the only ex-convict among the suspects. As Wanda knew about your prison sentence she began to suspect you when she first heard that a burglar who sharpened a knife had also freed a canary. She must have wondered then if you knew Ingelow. But she couldn’t be sure, and she was too frightened to talk. None of the others suspected you even after the murder because they didn’t know about your prison sentence or your motive. Of course, you never dreamed we would associate the freeing of the bird with your prison sentence, because you had never associated the two yourself. An irresistible, irrational impulse is neurotic, and a neurosis is by definition a failure to associate consciously an act with its emotional cause.”
Leonard Martin laughed. “Cobwebs and moonshine! Psychology is a joke to the layman, and juries are made up of laymen. The only things they believe are eye witnesses and material evidence—bloodstains and fingerprints. You haven’t got anything like that!”
“Murder is rarely performed before an eye witness. But we have material evidence far more conclusive than most fingerprints and bloodstains. That’s where the fly comes in.”
“The fly?”
“Do you know how the Hindus diagnose diabetes mellitus? There is an account of their procedure in Dr. Heiser’s autobiography. They set the patient’s urine outdoors in the sun. If it attracts flies they know it contains sugar and is therefore diabetic urine. The same sugar is present in the perspiration of a diabetic. When I first met you at the art gallery I saw you were a sick man. As I happen to be a doctor of medicine, I soon noticed the principal external symptoms of diabetes in you, just as I noticed that Pauline was anemic. You had the bronze skin of the diabetic in place of the prison pallor one expects to see in a man just out of prison. You had the extreme emaciation of the diabetic and his avoidance of sweet food. You refused French pastry at the art gallery, and you didn’t even take sugar in your coffee at Wanda’s this morning. Finally, there was the peculiar sweet, fruity odor of your breath which indicates butyric acid in the lungs.
“You wore no gloves when you clasped the handle of the knife you used to stab Ingelow, because Milhau had directed you to remove your gloves during the action of the play, and you couldn’t ignore his direction without rousing suspicion. In your character as a Russian detective, you had to wear heavy leather gloves—too heavy for such a delicate operation as stabbing Ingelow in a certain anatomical spot. But there was no danger of fingerprints, because you chose a knife handle that was elaborately grooved. Excitement and perhaps a recent dose of insulin made your palms perspire freely. The grooved surface of the knife handle rejected fingerprints, but it retained more perspiration than a smooth handle would have done. When a fly was attracted to the handle and ignored the bloodstained blade, I began to suspect the truth. The city toxicologist has already reported that he had found chemical traces of human perspiration and sugar on the knife handle. As soon as he subjects it to a spectroscope he will find some indication of butyric acid. This was the one fact Adeane knew that was not known to anyone else. He was the only witness present with the Inspector and myself when the fly alighted on the knife handle. He noticed it as we did and that cost him his life. This morning before rehearsal he told me in your presence that he had been reading about diseases of the pancreas at the medical library when he spoke of the suggestive effect on the body of such reading. He also mentioned Dr. Heiser’s book which he was carrying under one arm, and dropped a broad hint about the Fly who witnessed the murder of Cock Robin. Apparently he thought you could be bullied into helping his career. He wanted you to put two and two together—and you did. You knew from experience that diabetes was a disease of the pancreas, and you glanced through Adeane’s copy of Heiser’s book and saw that the only reference to flies concerned the Hindu method of diagnosing diabetes. You concluded as Adeane wanted you to, that he had read enough medical literature to recognize the symptoms of diabetes in you and that in some way the action of a fly had indicated to him that the murderer was a diabetic. But instead of allowing Adeane to blackmail you, you killed him; and he had so little realization of his danger that he gave you an opportunity to do so by playing Vladimir in order to bring himself and his plays to Milhau’s attention.”