DNA Alone Can't Tell Us Who Jack the Ripper Was

A new book published this week claims to have solved one of the greatest murder mysteries from before our time: the identity of Jack the Ripper. In Naming Jack the Ripper, "armchair detective" author Russell Edwards turns to modern forensics to offer what he reckons is definitive proof that the serial killer who terrorised East London in the 19th century was one Aaron Kosminski, a Polish immigrant in the city who has long been a favourite suspect in the case.

But while DNA testing has proved useful in shedding light on past puzzles—recently revealing a load of juicy historical factoids about Richard III, who roamed the country centuries before Kosminski (or whoever Jack really was)—there are still potential leaks in this recent claim that will keep London's Jack the Ripper tour guides and amateur sleuths in business for a while.

Writing in the Daily Mail on Sunday, Edwards explained that his evidence hinges on a scarf he bought at auction alleged to have belonged to Catherine Eddowes, one of the killer's victims. It was apparently bloodstained and unwashed, though Edwards admitted that "there was no evidence for its provenance," other than the previous owner claiming his ancestor had been a police officer at the scene of the crime way back in 1888.

That's a big red flag right off the bat, but Edwards hoped that by forensically analysing the stains on the garment, he could place it at the scene—or at least on the victim. He worked with Jari Louhelainen, a molecular biologist at Liverpool John Moores University, to analyse the DNA. While Louhelainen drew mitochondrial DNA out of the shawl, Edwards tracked down a descendant of Catherine Eddowes, the victim, who volunteered a DNA sample to compare it with. It was a match.

But while DNA testing is generally convincing, it's not foolproof. Steve Connor, science editor at the Independent, points out that the credibility of the "evidence" depends on the details of the analysis. He speculated that, as far as we know, the samples from the shawl could have been contaminated with the living relatives' samples. The methodology and results have not been published in a scientific journal or subject to any kind of peer review.

In any case, if confirmed, the blood stain only links a relative of Eddowes to the shawl. Not exactly proof of murder.

That's where more bodily fluids come in, and Edwards wrote that under UV light, Louhelainen found what looked like it could be a semen stain. Perhaps the shawl contained some Ripper DNA too.

He asked David Miller, a molecular andrologist at Leeds University, if he could detect any sperm cells in fibres from the shawl. Miller told me over the phone that he couldn't detect sperm cells specifically, but picked up some squamous cells. "I wasn't able to detect any sperm on it, but I did detect cells which I could recognise as possibly coming from skin, or perhaps from semen, or basically any secretory substance like saliva," he said.

Louhelainen used these cells in further DNA sequencing. Edwards tracked down a descendant of his suspect's sister, and Liverpool John Moores University reported that "Dr Jari Louhelainen matched DNA from the semen stains on the shawl to the descendant of Aaron Kosminski."

I asked Miller what the success rate was like for this kind of test—was this "proof"? "It's a standard forensic test," he said, and compared it to work done at contemporary crime scenes. In this case, he recovered about a half dozen squamous cells to work with. "Minute quantities of DNA were recovered in this instance and were then able to be matched against DNA that is much more abundantly available from a living relative, and the connection was made from there," he summarised.

"I was pleasantly surprised to see that a match was picked up," added Miller. It's particularly impressive given the length of time the cells must have been on the scarf, if they really were deposited there on the night of Eddowes' murder.

Without proof of provenance, it's impossible to say for sure how and when the cells, even if their identity is confirmed, got on the scarf. That's probably the biggest gap in the story, and it's one that DNA analysis can't necessarily help with. Even today, DNA at a crime scene doesn't tell you anything more than that someone's DNA is at the crime scene, and how compelling the evidence is depends on the details. Miller confirmed there was a risk the scarf could have picked up the cells elsewhere.

DNA analysis or no, enough time has passed that we'll probably always be able to preserve at least a modicum of doubt and mystery around the case. And it has to be said, Aaron the Ripper doesn't quite have the same ring to it.