“Because he did not want the maid to see him enter the house,” suggested Lestrade.

“Yet he conveniently left his revolver behind so that she could identify it, after having shown it to his brother in her presence?”

“Very careless of him,” conceded Lestrade.

“Yes…unbelievably so,” said Conan Doyle.   He paused for a moment, then added, “Secondly, how could he have climbed out and descended three storeys again, without being observed?   Surely the gunshot would have awakened the entire neighbourhood?”

“Well…yes,” muttered Lestrade, scratching his head in a bemused fashion.

“Surely it would have been much more effective to enter the house through the front door, kill Ian Douglas, kill the maid, Bridget, then leave through the front door again…Taking the murder weapon with him as he left?”

“And the third point?” I asked.

“If you will examine the broken window glass,” we all stooped to do so, “you will notice from the way that it has fallen to the side of the room, that the window could not possibly have been closed when the glass was broken.”

“What?” asked Lestrade and I together.

Looking more closely, we could both see what the great author meant.   The window was about eighteen inches away from the corner of the room, where the glass was scattered.   Instead of opening upwards or outwards, as most windows do, this one opened inwards, which meant that someone could stand behind the opened window, while standing in the bedroom.

After considering this fact for a moment, Lestrade said, “Then it had to have been broken by the killer, after the murder had been committed?”

“A fair enough assumption,” agreed Conan Doyle.   “It is rather unlikely that Ian Douglas would have just stood by and watched while the killer went through such an elaborate rigmarole.”

“But all of this points toward Andrew Douglas, not away from him,” insisted Lestrade.   “Because, if the killer did not enter the house by way of the window, then he must have been admitted by the murdered man.   And it would have been in Andrew Douglas’s best interests to make it look as though the killer had climbed in through the window.”