If the murderer had gone that way he would have found the door at the bottom locked, and the key removed, and he must have been caught before he could get back upstairs." "There's something in that," said Merrington.

"But how do you account for the door being unlocked in the first instance ?" "The servants know where the key is kept.

One of the maids may have taken it to steal out of the house that way to keep an appointment with a sweetheart, and forgotten all about it when she returned.

The back staircase and entrance are never used by the members of the household, and the key, which was inside the door, may have been there for days without being noticed.

Tufnell admits that it was only by chance he tried the door yesterday.