Presumably for heightened tension - first-order logic:

As an aside, it's worth pointing out that - presumably for heightened tension - in most Sherlock Holmes books, the murderer confesses, either by sobbing into a cup of tea and coming quietly, or by trying to kill Holmes, Watson, the hapless inspector Lestrade or all three are. Because of that the case never really has to go to trial. Just once, I'd like to see the lawyers got involved, and to see the spectacle of Holmes trying to rationalize his reasoning. This could be disastrous as at any expectation but his deductive reasoning was unsound.

Imagine a good lawyer pointing out that all five victims happened - entirely coincidentally - to be members of the silk glove appreciation society.....

Automating Reasoning is a very important topic in "AI", which has received much attention, and has found applications in the verification of hardware and software configurations, amongst other areas.