In the autumn of 1888, in the midst of a grisly string of murders, the Central News Office in London, Scotland Yard and government officials began receiving a string letters.

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“Dear Boss,” one postmarked on the 25th of September began. “I keep on hearing the police have caught me but they won’t fix me just yet.” The taunting letter, inscribed in red ink, was signed for the first time with a name that has sent shivers down generations of spines: “Jack the Ripper.”

Authorities ultimately received hundreds of letters, most of them obvious hoaxes, purporting to be from the serial killer. But there remains a fierce debate among researchers whether those initial letters received by authorities were authentic. Now, as George Dvorsky at Gizmodo reports, a forensic linguist has concluded that at least two of the letters were likely written by the same person—and that person was probably not the Ripper.

According to a press release, University of Manchester researcher Andrea Nini decided to analyze 209 letters signed by Jack the Ripper, including two of the earliest and most important writings. One of those is that “Dear Boss” letter, where the murder promises to clip off the ears of the next victim. In fact, the next victim did have one of her earlobes severed. The other is a blood-stained postcard which predicts a double murder and refers to the killer in the third person as “Saucy Jacky.”

Using forensic techniques, Nini examined the texts, finding that both “Dear Boss” and “Saucy Jacky” share some distinctive linguistic constructs, including the phrase “to keep back” instead of “withhold.” The research appears in the journal Digital Scholarship in the Humanities.

“Even though the ‘Dear Boss’ letter was not in the public domain when the Saucy Jacky postcard was received, they present a level of linguistic similarity—in terms of combination of words in common—that is much higher than one would expect if they were completely unrelated,” Nini tells Dvorsky. “The combination of words in common between the two letters are distinctive, so that one would not expect them to be shared by chance alone.”

According to the press release, previous handwriting analysis had also linked the two letters to the same writer. But Nini found that linguistic analysis possibly linked those two letters to a third, known as the “Moab and Midian” text. That letter has long been believed by some researchers to be a hoax.

If “Dear Boss,” “Saucy Jacky” and “Moab and Midion” are linked, that lends credence to the “journalist theory” that the early letters—including the ones that coined the term Jack the Ripper—were written by London newspapermen to keep the story alive. Theorists have long believed that a Central News Agency reporter named Thomas Bulling may have been behind it. Another journalist named Fred Best is also a possible suspect in writing the letters.

If the letters were a hoax and no murderer actually contacted authorities and dubbed himself “Jack the Ripper,” it means that after 130 years of research and investigation, we still know very little about the murders and whether the five supposedly “canonical” Jack the Ripper victims of the 11 murders committed in London’s East End—collectively known as the “Whitechapel Murders”—are linked.

Cold case though it may be, this doesn’t mean people aren’t still trying to crack the mystery. Twenty-five years ago, researchers discovered a diary kept by Liverpool cotton merchant James Maybrick in which he confesses to killing five women in London’s East End and another in Manchester. He signs the diary "Jack the Ripper." While the diary has long been considered a sophisticated forgery, and one man even confessed to creating it, last year some “Ripperologists” claimed they had evidence that the diary was found under the floorboards of Maybrick's home, which would seem to authenticate it.

Also last year, members of the team that uncovered Richard III’s grave in Leicester made an unsuccessful attempt to find and exhume the grave of Mary Kelly, widely believed to be Jack the Ripper’s last victim.