A killer normally commits twenty errors, but is only aware of a third of them. Most of them are due to carelessness or inexperience. But there's one type of error that we can consider deliberate. It's a sort of signature. "The devil's dumbest sin is vanity". But where's the fun in being the devil if you can't let anyone else know?
No man should ever confess to a crime he did not commit.
— What precisely is Michael's crime?
— He's my younger brother.
Indeed, I have found that it is usually in unimportant matters that there is a field for the observation, and for the quick analysis of cause and effect which gives the charm to an investigation. The larger crimes are apt to be the simpler, for the bigger the crime the more obvious, as a rule, is the motive.