Philo Vance
I think I have the whole thing. Now, follow me closely. The Canary was lying there. Spottswoode, let us say, was standing here, making a final plea for his boy, which met but an absolute refusal.
He walked around to the head of the sofa. Suddenly, he clapped his hand over her mouth, and with his other hand, caught her necklace, and before she had a chance to cry out, he strangled her.
He then proceeded to set the stage to make it appear that the crime had been committed with robbery as a motive. He stripped her jewels from her, and placed them in his pocket. Then, he took a cigarette from that box and lit it. He laid her hand here. Placed the cigarette between her fingers, so that in case anyone should look through the keyhole of that door, there, it would appear as if she were lying here smoking. He then overturned the entire apartment to make it look as if a burglar had ransacked the place.
Now, just step over here, Markham. He came to this closet door but he couldn't open it. Skeel had locked himself in, though Spottswoode didn't know that. And Skeel, through the keyhole, saw everything that Spottswoode did. That accounts for the orderly condition of this one closet, but everything else in the apartment was ransacked. And that, Markham, was the technique of the crime itself.