It would thus be possible for the person who inhabited these rooms to go away at seven o'clock in the evening and leave a light which would burn until past one in the morning and then extinguish itself.

This, of course, was only surmise, but it destroyed the significance of the night porter's statement.
"But, if the person who inhabited these chambers was not Jeffrey, who was he?
"The answer to that question seemed plain enough.

There was only one person who had a strong motive for perpetrating a fraud of this kind, and there was only one person to whom it was possible.

If this person was not Jeffrey, he must have been very like Jeffrey; sufficiently like for the body of the one to be mistaken for the body of the other.

For the production of Jeffrey's body was an essential part of the plan and must have been contemplated from the first.