By Steven Shukor
BBC News website, London
Chief Inspector Donald Sutherland Swanson went to his grave convinced of the true identity of Jack the Ripper.
Mr Swanson believes his great-grandfather identified the Ripper
Fortunately, he did not take the name of the suspect with him.
As the officer-in-case, Mr Swanson had the opportunity to review all the paperwork on the killer, whose identity has never ceased to obsess the public.
Around 1910, he was presented with a book by Assistant Commissioner Robert Anderson who was retiring from the Metropolitan Police, called The Lighter Side of My Official Life.
Beside passages where Dr Anderson dealt with the Ripper case, are several lines of pencil-written notes by Mr Swanson.
He elaborates on Mr Anderson's thoughts with comments such as "after this identification which suspect knew, no other murder of this kind took place in London".
But it is at the end of the book, on a blank page, where Mr Swanson reveals - as though it were his last words on the case - the suspect's name.
"...In a very short time the suspect with his hands tied behind his back, he was sent to Stepney Workhouse and then to Colney Hatch and died shortly afterwards - Kosminski was the suspect - DSS."
Polish-born Aaron Kosminski is not a new name among the countless suspects identified by police, journalists and historians down the years.
He became a suspect after he was allegedly spotted at the scene of the murder of Elizabeth Stride, believed to be the Ripper's third victim.
The existence of the book was made public in 1981
Kosminski, a hairdresser who arrived in England in 1882, had a history of mental illness and is once alleged to have threatened his sister with a knife.
Both Mr Anderson and Mr Swanson were convinced Kosminski was their man but claim he was never prosecuted because the sole witness apparently refused to testify against a fellow Jew.
Mr Swanson writes: "...because the suspect was also a Jew, and also because his evidence would convict the suspect, the witness would be the means of murderer being hanged which he did not wish to be left on his mind."
Mr Swanson claims there were no new Ripper murders once Kosminski knew he had been identified as a suspect.
Historical researcher Keith Skinner, an expert on the Ripper murders, says there are inconsistencies in Mr Swanson's notes, such as his claim that Kosminski died at Colney Hatch in the 1890s.
In fact, he died at Leavesden Asylum, in north London, in 1919.
"I'm not sure Aaron Kosminski is the right person," says Mr Skinner.
There were some "contradictions and conflicts" in Swanson's margin scribblings.
Mr Anderson's book was presented to Scotland Yard's Crime Museum to mark its re-launch by Mr Swanson's great-grandson, Nevill, 68, from Worcester.
He says the book was discovered when his father inherited the belongings of Mr Swanson's daughters and it became public knowledge in 1981.
He says he is proud that his great-grandfather had left his mark on such a high-profile case.
"He reviewed the case," he says. "He knew more about it than anybody else. His conclusion was that Aaron Kosminski was the killer.
"He was a very thorough man and I believe he reached the right conclusion."
Case closed? Probably not, says Det Ch Supt Steve Lovelock, head of the Metropolitan Police's crime academy.
"The mystery will probably never be solved," he says. "But maybe that's what makes the Jack the Ripper case so fascinating."