Singularity is almost invariably a clue. The more featureless and commonplace a crime is, the more difficult it is to bring it home.
Problems may be solved in the study which have baffled all those who have sought a solution by the aid of their senses.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.
I confess that I have been as blind as a mole, but it is better to learn wisdom late than never to learn it at all.
Circumstantial evidence is a very tricky thing. It may seem to point very straight to one thing, but if you shift your own point of view a little, you may find it pointing in an equally uncompromising manner to something entirely different.