"We have looked. It cannot be found. The murderer took it away. He would not be such a fool as to leave that lying about. The doctor fancies from the nature of the wound that it must be a long slim dagger--a kind of stiletto."
"Such as a foreigner might use," said Laura involuntarily.
"What do you mean?" asked the inspector sharply.
Laura flushed. "Nothing, nothing," she responded; "but foreigners usually make use of such a weapon, don't they? An Englishman would not kill a person with a stiletto."
"It's not British, certainly," said Derrick, with insular prejudice; "but a woman might use such a thing. Still, we do not know that the assassin is a man or"--he looked straight at her--"a woman."
Laura could not quite understand his meaning, since it never struck her that he meant to incriminate her in the matter. She took no notice, being anxious to learn what Derrick thought. "What is your theory on existing facts?" she asked coldly.
Derrick reflected. "I hardly know what to say. Let us suppose that the woman admitted herself into the house. How she got the latch-key I am not prepared to say. She came to meet some one--possibly the two people who killed her."
"The two people?" interrupted Laura abruptly.
"There was the young man who kept Mulligan in talk," explained the officer, "and the one who presumably killed her. Let us suppose, for the sake of argument, that this woman met these two men. Seeing a policeman at the gate, Number One goes out to lure him away. Left alone with Number Two, the woman sits at the piano to sing. On the music-stand is 'Kathleen Mavourneen.' She knows that song and sings it. The assassin, standing behind her, watches his opportunity and stabs her. Then he goes."
"You forget that the song was being sung, according to your own account, before Number One left the gate with the policeman."