Was there anything to tell one?
In the material sense, no.
There were no tangible clues - no fingerprints, no incriminating papers or documents.
There were only - the people themselves.
"And one tangible clue, the bridge scores.
"You may remember that from the beginning I showed a particular interest in those scores.
They told me something about the various people who had kept them, and they did more. They gave me one valuable hint.
I noticed at once, in the third rubber, the figure of 1500 above the line.
That figure could only represent one thing - a call of grand slam.
Now if a person were to make up his mind to commit a crime under these somewhat unusual circumstances, that is, during a rubber of bridge, that person was clearly running two serious risks.
The first was that the victim might cry out, and the second was that even if the victim did not cry out, some one of the other three might chance to look up at the psychological moment and actually witness the deed.
"Now as to the first risk, nothing could be done about it. It was a matter of a gambler's luck.
But something could be done about the second.
It stands to reason that during an interesting or an exciting hand the attention of the three players would be wholly on the game, whereas during a dull hand they were more likely to be looking about them.
Now a bid of grand slam is always exciting.
It is very often, as in this case it was, doubled.
Every one of the three players is playing with close attention - the declarer to get his contract, the adversaries to discard correctly and to get him down.
It was, then, a distinct possibility that the murder was committed during this particular hand, and I determined to find out if I could exactly how the bidding had gone.
I soon discovered that dummy during this particular hand had been Doctor Roberts.
I bore that in mind and approached the matter from my second angle - psychological probability.
Of the four suspects Mrs. Lorrimer struck me as by far the most likely to plan and carry out a successful murder - but I could not see her as committing any crime that had to be improvised on the spur of the moment.
On the other hand her manner that first evening puzzled me.
It suggested either that she had committed the murder herself or that she knew who had committed it.
Miss Meredith, Major Despard, and Doctor Roberts were all psychological possibilities, though, as I have already mentioned, each of them would have committed the crime from an entirely different angle.
"I next made a second test.
I got everyone in turn to tell me just what they remembered of the room.
From that I got some very valuable information.
First of all, by far the most likely person to have noticed the dagger was Doctor Roberts.
He was a natural observer of trifles of all kinds - what is called an observant man.
Of the bridge hands, however, he remembered practically nothing at all.
I did not expect him to remember much, hut his complete forgetfulness looked as though he had had something else on his mind, all the evening.
Again, you see, Doctor Roberts was indicated.
"Mrs. Lorrimer I found to have a marvelous card memory, and I could well imagine that with anyone of her powers of concentration a murder could easily be committed close at hand and she would never notice anything.
She gave me a valuable piece of information. The grand slam was bid by Doctor Roberts quite unjustifiably and he bid it in her suit, not his own, so that she necessarily played the hand.
"The third test, the test on which Superintendent Battle and I built a good deal, was the discovery of the earlier murders, so as to establish a similarity of method.
Well, the credit for those discoveries belongs to Superintendent Battle, to Mrs. Oliver, and to Colonel Race.
Discussing the matter with my friend Battle he confessed himself disappointed because there were no points of similarity between any of the three earlier crimes and that of the murder of Mr. Shaitana.
But actually that was not true.
The two murders attributed to Doctor Roberts when examined closely and from the psychological point of view and not the material one, proved to he almost exactly the same.
They, too, had been what I might describe as public murders.
A shaving brush boldly infected in the victim's own dressing-room while the doctor officially washes his hands after a visit.
The murder of Mrs. Craddock under cover of a typhoid inoculation.
Again done quite openly - in the sight of the world as you might say.
And the reaction of the man is the same.
Pushed into a corner, he seizes a chance and acts at once - sheer, bold, audacious bluff - exactly like his play at bridge.
As at bridge, so in the murder of Shaitana he took a long chance and played his cards well.
The blow was perfectly struck and at exactly the right moment.
"Now just at the moment that I had decided quite definitely that Roberts was the man, Mrs. Lorrimer asked me to come and see her - and quite convincingly accused herself of the crime!
I nearly believed her!
For a minute or two I did believe her, and then my little gray cells reasserted their mastery.