"Well, Stephen, or someone else, killed him. You remember the valet telling us that he came along, and tried the door, and found- it locked? Suppose the murderer was still in the room then?"
"All right, I'm supposing it. So what?"
The Sergeant caressed his chin. "I haven't worked it all out, but it does strike me that he may have thought he'd got to leave that door locked when he left the room."
"Why?"
"Might be the time element, mightn't it? He may have thought that if anyone was to come along and try the door a minute or two later, and find it unlocked, he'd be whittling down the time of the murder a bit dangerously. I don't say I quite see -"
"No, nor anyone else," interrupted Hemingway.
"There might have been a reason," persisted the Sergeant doggedly.
"There might have been half a dozen reasons, but what you seem to forget is that it isn't all that easy to turn keys from the wrong side of the door. If the door was locked from the outside, the man who did it must have provided himself with a tool for the purpose. He couldn't have done it extempore, so to speak."
"He could, by slipping a pencil through the handle of the key, with a bit of string attached."
"He could, but we haven't any evidence to show that he did. In fact, we've plenty of evidence to show that he didn't."