The man got into the house between four-thirty and six; that is to say, between dusk and the time when the bridge was raised.

There had been some visitors, and the door was open; so there was nothing to prevent him.

He may have been a common burglar, or he may have had some private grudge against Mr.
Douglas.

Since Mr.Douglas has spent most of his life in America, and this shotgun seems to be an American weapon, it would seem that the private grudge is the more likely theory.

He slipped into this room because it was the first he came to, and he hid behind the curtain.
There he remained until past eleven at night.