DNA evidence “proving” Jack the Ripper was a Polish barber isn’t enough to be conclusive

DNA analysis of evidence from the scene of one of the infamous Whitechapel murders has allegedly “proved” the identity of the Ripper – but it’s not an open-and-shut case.

Over the weekend, the Mail ran a feature claiming that the identity of Jack the Ripper - the most notorious serial killer in history - had been "unmasked" thanks to DNA samples found on a shawl next to the body of Catherine Eddowes, one of the Ripper's supposed victims. The piece is by Russell Edwards, who writes that he paid "a great deal of money for it" because of an "armchair obsession" with Ripper history, and only later did he realise that stains on the fabric might reveal clues as to the Ripper's identity.

Who was Jack the Ripper, then? Aaron Kosminski, we're told, a Polish barber who lived in Whitechapel at the time of the murders, and who had been named as a suspect in the initial investigation. DNA evidence on the shawl - taken from blood and semen stains - putting Kosminski at the scene of one of the murders shows "without reasonable doubt" (the Mail's words, not Edwards') that he was the Ripper. 

It's a compelling story, and sales of Edwards' new book (Naming Jack The Ripper) will no doubt get a tidy sales boost thanks to the publicity. It can't hurt his company, either - a Jack the Ripper souvenir and walking tour shop, based in Whitechapel. (The Mail doesn't include a disclaimer noting this, merely calling him a "businessman".)

That's the problem. This isn't a peer-reviewed piece of evidence that's gone through typical investigative channels. Edwards has a financial incentive to make his discovery look more impressive than it is - which isn't to say that he's lying, or that the respected forensic scientists who conducted the analysis are wrong, but just that it's just one further piece in a puzzle that's perhaps unsolveable. There have been loads of bits of "evidence" to have surfaced over the year which were supposed to settle the matter once and for all, but they never have, because the Ripper case is far more complex than many true crime obsessives are willing to admit.

For example:

The shawl's provenance is unclear
According to Edwards, the shawl at the centre of the claim was originally found next to the body of Catherine Eddowes by acting sergeant Amos Simpson, who was given permission by his superior officer to take it home as a gift for his wife, a dressmaker. Amos' descendant, David Melville-Hayes, lent it to Scotland Yard's Crime Museum from 1991 to 2001 - but then he reclaimed it, taking it on tour to Ripper conferences and providing it to a Channel 5 documentary in 2006 for "inconclusive" swabbing.

There's also no real proof that the shawl has been in Melville-Hayes' family since Simpson found it - if it was a gift for a dressmaker, why wasn't it used? Can we be sure that the shawl, if it existed, wasn't confused with another piece of fabric? - nor that the shawl was actually found next to Eddowes' body. Among Ripper historians there's a fair bit of doubt that Simpson was, as he claimed, one of the first officers on the scene of the crime, as the family legend doesn't tally with the official crime report. It's telling that Scotland Yard's Crime Museum didn't consider the shawl to be authentic evidence and never put it on display, a detail brushed over in the story.

DNA is fragile and misleading
The processes for bagging and tagging evidence at crime scenes is meticulous for a very good reason - DNA is fragile, and contamination of evidence is easy. It's somewhat surprising, then, to notice an important detail in the photograph of Edwards holding up the shawl in the Mail piece. He's not wearing gloves.

Even accepting the story that the shawl was never washed and left in a cupboard somewhere for 126 years, that isn't enough to guarantee that it hasn't been contaminated. The Times reports that three of Eddowes' direct descendants were in the same room as the shawl in 2007 during a Ripper conference, and that they may have been among dozens of people who are known to have handled it.

The analysis of the genetic material on the shawl was conducted by Jari Louhelainen of Liverpool John Moores University, a respected expert within his field, working in his spare time. He hasn't published his work in a journal so we can't inspect and assess his method, so we've only got what he wrote in the Mail to go on: he extracted DNA samples from the two stains on the shawl (using a technique he invented), then used a conventional polymerase chain reaction to duplicate the samples until a large enough amount was secured for sequencing. The blood stain matched samples taken from descendants of Eddowes, while the semen stain matched a female descendant of Kosminski's sister.

Except, they only sort of matched. In a case like this identification has to be done with mitochondrial DNA, the part of the genome which is passed down along the mother's line and which doesn't mutate with each generation - and, since Kosminski and Eddowes aren't around any more, matching up their mitochondrial DNA to those of people alive today is the best chance to prove identity. The problem with this, though, is that it merely proves a mitochondrial DNA match. Even if we assume that the shawl hasn't been contaminated over the years, it doesn't prove anything more than a Kosminski's semen and an Eddowes' blood is on the shawl.

It's not hard to imagine how that might happen. Kosminski was admitted to an asylum three years after the Whitechapel Murders for poor mental health - he suffered from auditory hallucinations, ate rubbish and refused to wash himself - and was known to be, as the Victorians euphamised, a "self-abuser". He could have masturbated on the shawl and then thrown it away, at which point Eddowes (whom Edwards points out was so poor she had to pawn her shoes) may have spotted it and picked it up, only to be murdered while wearing it later. Kosminski also lived in Whitechapel with his two brothers, either of whom could also have been the source of the semen stain - any of the three could have been one of Eddowes' clients. 

Kosminski's only prior connection to the Ripper murders is that the surname Kosminski - but no first name - was listed as a suspect in notes never meant for the public by some of the officers involved in the investigation. Aaron Kosminski both lived in Whitechapel at the times of the murders and was later admitted to Colney Hatch Asylum, but as he lived nearly 20 years beyond the date the police believed that their Kosminski suspect died, it's not unlikely that there could be a case of mistaken identity. (Compounded by the large number of Polish-born Yiddish-speaking Jews living in the crime-ridden East End at the time, and the tendency of residents of the area to use aliases to avoid suspicion from the authorities.)

Cross-contamination in the lab is also a persistent fear in these kinds of cases, where a sample from a piece of evidence is processed in the same room (and maybe even with the same equipment) as the sample it's to be compared to, and the "match" is a mistake that comes from accidentally comparing a sample to itself. Without knowing Louhelainen's precise methodology, and without further analysis by another lab to control for cross-contamination, we can't rule this out.

Essentially, even if the DNA matches are correct, the very best this proves is that at some point Kosminski and Eddowes were in the presence of the same piece of fabric. This is evidence as part of a wider case, but not proof of guilt in itself.

Jack the Ripper, wasn't
It makes for good headlines and it brings tourists to the East End, but much of the public's perception of Jack the Ripper is more a reflection of press hysteria than the reality of the murders that took place. Many of the attempts to identify Jack the Ripper ignore the possibility that he never existed.

Between April 1888 and February 1891 there were eleven murders of poor women in Whitechapel which the Metropolitan Police grouped togethered into a single investigation, and of which five are usually attributed to Jack the Ripper. The case has been made, though, that as few as three of these were by the same person, while others have maintained that a number of other attacks and murders around the same time may have also been the Ripper's work. The issue here is that, for example, the death of Elizabeth Stride on 30 September - only an hour or so before Eddowes was also killed - is included as a Ripper killing because of a postcard claiming responsibility for both that was sent to the Central News Agency more than a day after the event. That postcard is widely believed to be a hoax, but it's also the source of the name "Jack the Ripper". This is the irony - the infamous details are also untrustworthy.

Even if Kosminski was responsible for Eddowes' death, it is still the case that there were likely many murderers stalking the streets of Whitechapel in the late 19th century. The truth of all that violence cannot be held within one piece of cloth.

Ian Steadman is a staff science and technology writer at the New Statesman. He is on Twitter as @iansteadman.