For over one hundred years, the identity of the notorious serial killer Jack the Ripper, who terrorized London in the late nineteenth century, has been a mystery that’s haunted both criminologists and history buffs alike, becoming the stuff of popular folklore.

However, new DNA tests from the scene of Jack’s crimes are believed to have blown the lid off of the mystery once and for all, revealing the butcher to have actually been a 23-year-old barber from Poland named Aaron Kosminski.

A forensic study of semen left behind on a blood-stained silk shawl near victim Catherine “Kate” Eddowes has convinced at least one team of scientists that the likely killer was the Polish immigrant.

Kosminski had previously been tagged as the killer in a 2014 study of the shawl by Dr. Jari Louhelainen, a Liverpool John Moores University molecular biology professor and co-author of the most recent study. However, at that time genetic researchers could not acquire the details about the investigation and thus were unable to independently verify the claim.

Yet Louhelaine and his fellow researcher Dr. David Miller, a reader in molecular andrology at the University of Leeds, were able to continue testing the shawl and match the mitochondrial DNA from blood and sperm samples to both the living descendants of the alleged killer and the victim. They are now sure that the shawl is the key piece of evidence linking the Polish barber to the crime.

The researchers described their findings in the Journal of Forensic Sciences, where they wrote:

“We describe for the first time systematic, molecular level analysis of the only surviving physical evidence linked to the Jack the Ripper murders.

Finding both matching profiles in the same piece of evidence enhances the statistical probability of its overall identification and reinforces the claim that the shawl is authentic.”

The serial killings tied to Jack the Ripper began in August 1888 and ended in November—claiming the lives of at least five women.

Eddowes was killed in a grisly murder in Mitre Square, Whitechapel on the night of September 30, 1888—when her cheeks were shredded by the Ripper and her kidney removed. It has long been rumored that the victim’s kidney was eaten by the killer, who had slit another woman’s throat earlier that night in an episode known as the “Whitechapel killings.”

A businessman named Russell Edwards bought a shawl believed to be stained with Eddowes’ blood at an auction in 2007 before contacting the scientists.

While Kosminski had previously been linked to the serial killings, police were unable to pursue charges at the time due to a lack of sufficient evidence and the fact that a witness who identified one of his killings was unwilling to testify against him. The alleged killer was released back into the custody of his family.

Critics, however, remain skeptical that the new findings conclusively prove that Kosminski is the culprit. Science magazine has published criticisms of the researchers’ methodology to the effect that the mitochondrial DNA tests can only rule out suspects rather than positively identify them, while the UK Data Protection Act prevents other scientists from verifying the genetic data due to its private nature.

Other critics have also noted that the shawl may have never been at the crime scene at all, or has become contaminated in the 130-plus years since the murder.