My next business I decided must be to find the present whereabouts of the “Odd Trick,” but before setting out to do so I had a point of some importance to consider. Every one who has studied criminology knows that each individual criminal has certain methods which are repeated with very little variation in consecutive crimes. The circumstances may so vary as to cause the features of the crime to have a different aspect from the feature of any previous crime, but the methods pursued are generally the same. The criminal classes are almost invariably creatures of habit. The fact that a certain method--be it adopted for the purpose of committing a crime, concealing a crime, or of effecting the criminal’s escape--has proved successful in the past is to them the strongest possible reason for again adopting the same method. They associate that method in their thoughts with what they call their luck, and shrink from having to depart from it. Hence the detective-psychologist should be quick to get what I may--with no sinister meaning in regard to after events--be allowed to call the “hang” of the criminal’s mind, and to discover the methods which, though varying circumstances may necessitate their being worked out in varying ways, are common to most of his crimes. The detective who can do this has his antagonist at a disadvantage. He is like the hunter who knows that the hare will double, or that this or that quarry will try to set the hounds at fault and seek to destroy the scent by taking to the water. And just as the hunter’s acquaintance with the tricks of the quarry assists him to anticipate and to forestall the poor beast’s efforts to escape, so the detective who has taken a criminal’s measure, and discovered the methods upon which he works, can often turn the very means which are intended to effect an escape into means to effect a capture. I need not point out to the observant reader that Mullen’s one anxiety in all his movements was to cover up his traces. He could be daring and even reckless at times, as witness this fact of his having gone away in a boat, which, should his connection with Mrs. Burgoyne leak out, would, as I have already said, be the very first object of inquiry. It would seem, in fact, as if, so long as he had satisfied himself that he had left no “spoor” behind, he preferred adopting a bold course to a timid one, as for instance when he openly proclaimed the murder of Green to be the handiwork of Captain Shannon by leaving a declaration to that effect folded up in a bottle which was attached to the body.