I suppose it fitted in somehow with his character.

It reminded him, you see, of his favourite roses, and, as HE whistled it, it was the most melancholy tune going.
Turning from the window, after a minute or two, the Sergeant walked into the middle of the room, and stopped there, deep in thought, with his eyes on Miss Rachel's bed-room door.

After a little he roused himself, nodded his head, as much as to say, "That will do," and, addressing me, asked for ten minutes' conversation with my mistress, at her ladyship's earliest convenience.
Leaving the room with this message, I heard Mr.Franklin ask the Sergeant a question, and stopped to hear the answer also at the threshold of the door.
"Can you guess yet," inquired Mr.Franklin, "who has stolen the Diamond ?" "NOBODY HAS STOLEN THE DIAMOND," answered Sergeant Cuff.
We both started at that extraordinary view of the case, and both earnestly begged him to tell us what he meant.
"Wait a little," said the Sergeant.

"The pieces of the puzzle are not all put together yet.".