At this, since George wouldn't accompany me, I myself thoroughly examined all the windows of the apartment. I have, I am sure, what is known as the "detective instinct." I am of the conviction that it is scarcely possible for a human being to be in a room, even for a short time, and go from it without leaving behind him some evidence of his having been there. So I made a round of the rooms. I scrutinized every window. The only ones I found open were those which Charlotte had said she had herself opened that morning. The others were securely fastened with an ingenious contrivance which was really burglar-proof. Granting Charlotte's assertions to be true, which I had no reason to doubt, the net was surely drawing closely around these two women. But I felt sure there was some other possibility, and I determined to discover it.
There was no back stair or kitchen exit. The dumb-waiter had a strong snap bolt and closed itself, without any means of opening from the other side. Then I returned and carefully examined the front door. The Hale lock, though easily opened with its own key, was not to be opened otherwise; and, aside from this, a key was of no use if the night-chain was on. I looked at the heavy brass chain; then I put it in its slot, and opened the door the slight distance that the chain allowed. The opening was barely large enough to admit my hand. There was no possibility of a man getting through that tiny crack, nor could he by any chance put his hand through and slide the chain back; for to remove the chain I had to close the door again, as Charlotte had done this morning.
For the first time I began to feel that I was really facing a terrible situation.
If only I had kept silent about that chain, and if Janet and Charlotte had also failed to mention it, there would have been ample grounds for suspecting that an intruder had come in by the front door.
But realizing myself that the windows had all been secured, and that the chain had been on all night, what possibility was left save the implication of one or both of the only human beings shut inside with the victim?
Bah! There must be other possibilities, no matter how improbable they might be. Perhaps an intruder had come in before the door was chained, and had concealed himself until midnight and then had committed the crime.
But I was forced to admit that he could not have put the chain on the door behind him when he went away.
I even tried this, and, of course, when the door was sufficiently ajar to get my hand through, I could not push the end of the chain back to its socket. The door had to be closed to do this.
With a growing terror at my heart, I reviewed other possibilities. Perhaps the intruder had remained in the house all night, and had slipped away unobserved in the morning.
But he couldn't have gone before Charlotte unchained the door, and since then there had been a crowd of people around constantly.