There have, however, been occasions when detection has failed more or less completely. The police do not admit always that the perpetrators remain unknown; they have clues, suspicion, strong presumption, even more, but there is a gap in the evidence forthcoming, and to attempt prosecution would be to face inevitable defeat. To this day it is held at Scotland Yard that the real murderer in a mysterious murder in London in the seventies was discovered, but that the case failed before an artfully planned _alibi_. Sometimes an arrest is made on grounds that afford strong _primâ-facie_ evidence, yet the case breaks down in court. The Burdell murder in 1857, in New York, was one of these. Dr. Burdell was a wealthy and eccentric dentist, owning a house in Bond Street, the greater part of which he let out in tenements. One of his tenants was a Mrs. Cunningham, to whom he became engaged, and whom, according to one account, he married. In any case, they quarrelled furiously, and Dr. Burdell warned her that she must leave the house, as he had let her rooms. Whereupon she told him significantly that he might not live to sign the agreement. Shortly afterwards he was found murdered, stabbed with fifteen wounds, and there were all the signs of a violent struggle. The wounds must [Illustration: OLD MILLBANK PRISON.] have been inflicted by a left-handed person, and Mrs. Cunningham was proved to be left-handed. The facts were strong against her, and she was arrested, but was acquitted on trial. It came out long after the mysterious Road (Somerset) murder that the detectives were absolutely right about it, and that Inspector Whicher, of Scotland Yard, in fixing the crime on Constance Kent, had worked out the case with singular acumen. He elicited the motive--her jealousy of the little brother, one of a second family; he built up the clever theory of the abstracted nightdress, and obtained what he considered sufficient proof. It will be remembered that this accusation was denounced as frivolous and unjust. Mr. Whicher was so overwhelmed with ridicule that he soon afterwards retired from the force, and died, it was said, of a broken heart. His failure, as it was called, threw suspicion upon Mr. Kent, the father of the murdered child, and Gough, the boy's nurse, and both were apprehended and charged, but the cases were dismissed. In the end, as all the world knows, Constance Kent, who had entered an Anglican sisterhood, made full confession to the Rev. Mr. Wagner, of Brighton, and she was duly convicted of murder. Although sentence of death was passed, it was commuted, and I had her in my charge at Millbank for years.