From Robert Adey's Locked Room Murders (Ferret Fantasy, London 1979)
Major discussions on the subject of locked room murders are to be found in Carr's The Hollow Man, Rawson's Death from a Top Hat and Holmes' Nine by Nine.
There appear to be some 20 different ways in which a locked room can be breached.
Analysis of solutions
3 Remote control – poison gas or impelled to do so with his own hands.
4 Mechanical and other devices.
6 Outside the agency made to look like inside agency. E.g. dagger fired through window.
7 Victim killed earlier but made to appear alive later.
8 Presumed dead but not killed until later, e.g., by the first person to enter the room.
9 Victim wounded outside, dies inside.
10 Turning key, bolt, catch, etc, from outside with pliers, string, etc
11 Unhinging and rehinging door or window.
12 Taking out and replacing windowpane.
13 Acrobatic manoeuvre,.
14 Door locked or wedged on outside. Key replaced or bolt thrown after re-entrance.
15 Door locked on outside. Key returned before re-entrance.
16 Other methods of gimmicking doors, windows etc.,
17 Secret passages, sliding panels, etc.,
18 Murderer still in room when entrance forced.
19 Alibi provided while murder committed in an apparently
20 Other impersonation stunts
A further mystery is the price and rarity of the much enlarged edition from Crossover Press 1992. A copy on Canadian Amazon (often a home for awesome prices) at $10000 seems to have now vanished...