“By all means,” I replied, a little uncomfortably.
“Well,” he said, “the position is this. A man has died in a certain house, to which he has been confined as an invalid for some considerable time. The cause of his death is stated to be poisoning by arsenic. That statement is made by a competent medical witness who has had the fullest opportunity to ascertain the facts. He makes the statement with complete confidence that it is a true statement, and his opinion is supported by those of two other competent professional witnesses. It is an established fact, which cannot be contested, that the body of deceased contained sufficient arsenic to cause his death. So far as we can see, there is not the slightest reason to doubt that the man died from arsenical poisoning.
“When we come to the question, ‘How did the arsenic find its way into the man’s body?’ there appears to be only one possible answer. Suicide and accident are clearly excluded. The evidence makes it practically certain that the poison was administered to him by some person or persons with the intent to compass his death; and the circumstances in which the poisoning occurred make it virtually certain that the arsenic was administered to this man by some person or persons customarily and intimately in contact with him.
“The evidence shows that there were eight persons who would answer this description; and we have no knowledge of the existence of any others. Those persons are: Barbara Monkhouse, Madeline Norris, Anthony Wallingford, the housemaid, Mabel Withers, the cook, the kitchen-maid, Dr. Dimsdale and Rupert Mayfield. Of these eight persons the police will assume that one, or more, administered the poison; and, so far as we can see, the police are probably right.”
I was rather staggered by his bluntness. But I had asked for his opinion and I had got it. After a brief pause, I said:
“We are still, of course, dealing with the depositions. On those, as you say, a presumption of guilt lies against these eight persons collectively. That doesn’t carry us very far in a legal sense. You can’t indict eight persons as having among them the guilty party. Do you take it that the presumption of guilt lies more heavily on some of these persons than on others?”
“Undoubtedly,” he replied. “I enumerated them merely as the body of persons who fulfilled the necessary conditions as to opportunity and among whom the police will—reasonably—look for the guilty person. In a sense, they are all suspect until the guilt is fixed on a particular person. They all had, technically, a motive, since they all benefited by the death of deceased. Actually, none of them has been shown to have any motive at all in an ordinary and reasonable sense. But for practical purposes, several of them can almost be put outside the area of suspicion; the kitchen-maid, for instance, and Dr. Dimsdale and yourself.”
“And Mrs. Monkhouse,” I interposed, “seeing that she appears to have been absent and far away on each occasion when the poison seems to have been administered.”
“Precisely,” he agreed. “In fact, her absence would seem to exclude her from the group of possible suspects. But apart from its bearing on herself, her absence from home on these occasions has a rather important bearing on some of the others.”
“Indeed!” said I, trying rapidly to judge what that bearing might be.