It's been called the world's most famous cold case, a source of endless fascination and speculation ever since the first mutilated victim was found in a bloody heap 123 years ago on the gas-lighted streets of East London.
So why is Scotland Yard suppressing information that some crime buffs think could offer fresh leads on the identity of Britain's most notorious serial killer, Jack the Ripper?
That's the question baffling Trevor Marriott, a retired homicide detective who's been waging a solitary legal battle to force "the Yard" to release uncensored versions of information recorded in thick Victorian ledgers that are gathering dust in an official archive.
The volumes contain tens of thousands of tidbits on the Yard's dealings with the public and police informants in the years that followed the Ripper's grisly two-month killing rampage in 1888. The shadowy figure is alleged to have slain five women in London's seamy Whitechapel district, slitting their throats and, in some cases, eviscerating them with almost surgical precision.
But the Metropolitan Police Service, as Scotland Yard is formally known, has staunchly refused to publish the documents in unexpurgated form, without names blacked out.
In a surreal tribunal hearing in May, which saw a senior officer give evidence from behind an opaque screen and cite Judas Iscariot to support his point, the agency argued that laying everything bare would violate its confidentiality pledge to informants, even those long dead, and undermine recruitment of collaborators in the present-day fight against terrorism and organized crime.
Naming names might even put the snitches' descendants at risk of revenge by the grudge-bearing heirs of those who were informed on, officials said. The three-person tribunal agreed.
And so the files continue to molder while Ripper enthusiasts like Marriott chafe, wondering what tantalizing clues remain hidden.
"There may be a little gem in there which corroborates something we already know," said Marriott, who has been working to unmask the killer since 2002. He has published a book outlining his own theory of whodunit centering on a lesser-known candidate who wound up convicted and executed for a brutal murder in the United States.
The ledgers, he said, could point out new avenues to dedicated "Ripperologists" and armchair detectives as they chase the solution to one of history's great unsolved mysteries.
Interest in the "Whitechapel murders" has seemingly never flagged since the gruesome crimes were committed toward the end of Queen Victoria's reign. The combination of sleaze (the victims were prostitutes), squalor (the East End was a den of poverty and drink), and blood and gore (buckets of it) has proved irresistible to amateur and expert sleuths alike.
Suspects at the time included an American quack who later fled London and a Polish Jew who lived in Whitechapel.
More recently, crime novelist Patricia Cornwell concluded in a 2002 book that Jack the Ripper was the painter Walter Sickert.
Conspiracy theorists finger a deranged member of the royal family and accuse Scotland Yard of colluding in a cover-up. And a Spanish author has just come out with a claim that the killer was a lead detective in the case.
"Unsolved murder — instantly everyone thinks, 'I can solve it,'" said Angela Down, a tour guide who has helped conduct a "Jack the Ripper Walk" around East London for 10 years. "We all love a mystery. If it were solved, all the interest would fall away."
The circuit is far and away the most popular attraction offered by tour company London Walks; on the nights that the walk is hosted by noted Ripper expert Donald Rumbelow, it can draw hundreds of participants.
As they meander through narrow streets and cross a square whose cobblestones were there when the fourth victim, Catherine Eddowes, was found dead, listeners are reminded that the name "Jack the Ripper" is almost certainly a hoax. A taunting letter purporting to be from the killer and signed "Jack the Ripper" was received by a news agency on Sept. 27, 1888, not long after the slaying of Annie Chapman, the second victim.
"Dear Boss," the letter began, before describing how the writer was "down on whores" and wouldn't "quit ripping them" until he was caught.
But the letter is now widely believed to have been the work of a tabloid journalist intent on making the story even more sensational than it already was. ("Nothing's changed," a woman murmured during the guided tour one recent evening.)
Marriott's theory, which he has put forth on the BBC and the National Geographic Channel, is that the killer was a German sailor named Carl Feigenbaum who eventually ended up in New York, where he cut the throat of his elderly landlady. Feigenbaum was executed in the electric chair in 1896, but not before telling his lawyer that he had always suffered from an uncontrollable urge to "kill and mutilate" women.
Shipping records show that the merchant seaman's vessel was docked in London at the time of the murders, close to Whitechapel, a red-light district likely to have been popular with sailors.
Marriott's research has uncovered similarly brutal killings in Germany that occurred a few years afterward.
As a police officer in Bedfordshire, north of London, Marriott maintained a cursory interest in the Ripper case but was more preoccupied with the murders he was investigating as a homicide detective.
He retired in the mid-'80s. Eight or nine years ago, in search of a hobby, he figured he would try his hand at the one riddle that ruled them all.
"I decided to look at it as a cold-case file," said Marriott.
"There are a lot of dedicated researchers and people who have followed the Ripper mystery, but nobody with any real professional knowledge or expertise had actually sat down or gone through it in any great detail," he said. "That's where I think my knowledge and expertise has helped look at this in a different light."
His quest has taken him around Europe and to North America. But Marriott is desperate to find fresh nuggets of information in the Scotland Yard ledgers.
After his request for access was denied in 2008, Marriott looked for help from the Information Commissioner's Office, which sided with Scotland Yard. He then took the matter before Britain's Information Rights Tribunal, which adjudicates appeals based on the Freedom of Information Act.
During the tribunal hearing in May, a senior officer identified only as "Detective Inspector D" said from behind a screen that the passage of time was not a good enough reason to reveal the names of informants.
"Look at one of the world's best-known informants, Judas Iscariot. If someone could draw a bloodline from Judas Iscariot to a present-day person, then that person would face a risk, although I know that seems an extreme example," the officer said, according to the Daily Telegraph newspaper.
Marriott rejects that argument, saying that it would be "almost 99.99% impossible to trace" the descendants of the informants, who are often identified in the registers by pseudonyms or by surnames only.
In July, the tribunal upheld the Yard's right to keep the files secret. In response to an appeal by Marriott, the panel reaffirmed its decision Aug. 31, which, coincidentally or not, was the 123rd anniversary of the death of the Ripper's first victim, Mary Ann Nichols.
Marriott's only remaining appeal would be to the home secretary or Queen Elizabeth. Chances of success: close to nil.
"I've spent fortunes on this case.... I don't know where we go now. I suspect this will probably be the end game," he said resignedly.
If so, what's in the ledgers "will be lost forever," Marriott said. And the identity of Jack the Ripper will vanish in the mists of time, like the London fog that swallowed up a bloody killer and left an enduring mystery eddying in his wake.