In Black Coffee by Agatha Christie (novel by Charles Osborne) Barbara Amory points to Hastings how in detective stories it is always the least likely suspect who turns out to be the murderer. Though the-least-likely-suspect-ploy is referenced within the story here even otherwise as reader of detective stories we know it to be the general rule. Murder mysteries are more of a game between the reader and the author rather than being mere engagement between their heart and soul.
So, how do we really follow a murder mystery. We don’t compare every witness’ account of the events neither are we mulling over those little and nicely masqueraded hints that are going to be pointed at by Mr. Poirot at the end. Methods and Order, Naah. What we actually do is that we are racing towards the end and hoping and hoping that the end will come out as a big surprise. In fact that is how we judge a suspense/ thriller. How big is the surprise! And for the end to be a surprise the killer has to be the one whom we suspect the least at the moment of the big revelation.
This is interesting as we see that ‘The least likely suspect’ hypotheses, which the reader as well as the author follow, is but a paradox.
The least likely suspect is the most likely to be the killer. But as he is the most likely suspect now, he becomes the least likely suspect. But again, since he has become the least likely, he is now the most likely and so on. So the variables, ‘the least likely suspect’ and ‘the most likely suspect’ will keep inter-changing themselves infinitely before any logical determinate conclusion is made.
Now for a surprise to happen, and we do get surprised, ‘the least likely or the less likely (set of) suspects’ must exist at that particular moment but then it can not exist because they are indeed indeterminable.