The "information received" with regard to ordinary crimes and ordinary criminals is of a different kind. The information on which the police as a rule act when they obtain a "clue" to a mystery is furnished from outside. Sometimes it comes from an acquaintance of the guilty person--as often as not, when the guilty person is a professional criminal, it comes from a jealous woman or from a "nark"--that is, from a person who mixes with a criminal set as one of themselves, and is all the time in constant communication with the police. "From information I received I went to such and such an address," is the conventional opening of the police officer's evidence. Very rarely does the real source of information transpire. For the police to give away a professional informer would be to lose an important ally in their war against crime. The deputy of a low lodging-house, the landlord of a public-house frequented by bad characters, would have to pay a heavy penalty if it were known that he was the person who told the police where to put their hand on the "wanted" man. Still worse would it fare with the women who, often when the proceeds of the job have been spent upon them, give Scotland Yard the "office" that So-and-so has been flush of money ever since the night of a certain burglary or shop robbery. Some of the most expert criminals in London always work single-handed. They might trust a "pal," but they mistrust a pal's pal, and they are especially prejudiced against his female acquaintances. In nine cases out of ten it is a woman who has given the first information to Scotland Yard when a professional criminal who has covered his tracks with the greatest success is suddenly pounced upon by an active and intelligent officer. Sometimes the betrayal is due to a quarrel in which the woman has been badly knocked about; sometimes it is due to jealousy, but as often as not the information comes from a woman who lives in the neighbourhood, who consorts with thieves, who is herself the wife or the sweetheart of a criminal, but is at the same time a spy acting for the police and in receipt of police pay. The subject is one upon which it is necessary to write with discretion. In the interests of justice a certain reticence is imperative in such a matter as this. If it were not so I might show how in some sensational cases which have recently been tried the guilty persons would never have been brought to justice but for an act of betrayal which was treacherous in the extreme. When one knows who committed a murder, to conceal that knowledge is to be an accessory after the fact. The law demands that the knowledge shall instantly be placed at the service of the police. I am not considering information given with regard to murder as treacherous. The cases I have in my mind are those in which the crime was incited by certain individuals who for purposes of their own intended to betray the criminal.