Chief Inspector Donald Swanson kept quiet for years but in retirement, frustrated that the murderer had escaped justice, could not resist scribbling notes in the margin of his boss’s memoirs, naming the man that they both believed had become the world’s most famous serial killer.

The man he named was Aaron Kosminski, a Polish-Jewish hairdresser living in Whitechapel, East London, who was eventually committed to a lunatic asylum, where he died.

According to Swanson the police were so convinced that Kosminski was the killer of at least five prostitutes in the 1880s that they organised a secret identity parade at a police rest home. The witness was a Jew who was said to have refused to give evidence.

Swanson made his notes in a book called The Lighter Side of My Official Life by Sir Robert Anderson, who was an assistant commissioner, for whom Swanson became staff officer.

Sir Robert said as a “definitely ascertainable fact” that the killer was a Polish Jew. He said that the only person who ever had a good view of the killer “unhesitantly identified the suspect the instant he was confronted but refused to give evidence”.

Mr Swanson wrote: “Because the suspect was also a Jew and also because his evidence would convict the suspect and witness would be the means of murderer being hanged — which he did not wish to be left on his mind.”

He said that the suspect had been taken by police to the rest home for the identification and that Kosminski knew he had been identified. He was taken back to his brother’s home in Whitechapel and police kept a secret watch.

Eventually he had to be taken, bound, to a workhouse and then to an asylum where he died “shortly afterwards”. Swanson wrote: “Kosminski was the suspect.”

Yesterday as the Swanson family handed over the book with its margin notes to the Yard’s refurbished Crime Museum, Detective Chief Superintendent Steve Lovelock, who heads detective training and the museum, said that the identification was very interesting.

Mr Lovelock said that the name had been mentioned before and the margin notes were revealed some years ago but he believed that they were significant.

Nevill Swanson, the Victorian detective’s grandson, said; “My grandfather thought he had got his man but never nailed him.”

Yard researches suggested that Kosminski was arrested by police after he threatened his sister with a knife and they were struck by his resemblance to descriptions of the Ripper.

But he was considered too mentally ill to be questioned, He was taken in the care of his brother to a Yard police rest home in Brighton and the identity parade was held there.

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