The answer was conclusive.

It told me that Drebber had already applied for the protection of the law against an old rival in love, named Jefferson Hope, and that this same Hope was at present in Europe.

I knew now that I held the clue to the mystery in my hand, and all that remained was to secure the murderer.
"I had already determined in my own mind that the man who had walked into the house with Drebber, was none other than the man who had driven the cab.

The marks in the road showed me that the horse had wandered on in a way which would have been impossible had there been anyone in charge of it.

Where, then, could the driver be, unless he were inside the house?
Again, it is absurd to suppose that any sane man would carry out a deliberate crime under the very eyes, as it were, of a third person, who was sure to betray him.