Me reading through Sherlock Holmes library for the first time (with the exception of hound of the Baskerville’s which I’ve read before): Strange. The mystery has been resolved but there’s still a good chunk of the book left
The villain: As you’ve bested me, mister Holmes and these constables shall surely take me to the scaffold, please let me tell you my humble life story in great detail.
It is interesting, and not unique to Doyle by any means.
I am currently reading my way through a lot of detective books by Doyle’s contemporaries (Boothby, Morrison, Meade & Eustace, Le Quex, Austin Freeman, Bramah, Futrelle, Reeve, AK Greene etc) and it is quite common for the culprit to be identified and arrested but for the story to then carry on at some length with a kind of “post mortem” where the detective explains what actually happened and how he worked it out.
It wasn’t really until Christie came along and showed how to organise the denouement so that the explanation comes first and leads up to revealing the culprit right at the every end.