Meet the soil detective solving Britain's coldest cases

When forensic soil scientist Professor Lorna Dawson stepped into the witness box during the trial of Christopher Halliwell, she knew her evidence could help convict the 52-year-old Swindon taxi driver as a multiple murderer. He stood accused of the rape and murder of 20-year-old Becky Godden more than a decade earlier and was already serving a life sentence for killing another young woman.

Lorna’s job was to explain to the jury in a clear and unbiased way how a few grains of soil found on a spade in Halliwell’s garden shed could link him to Becky’s shallow grave in a remote Gloucestershire field. It’s largely thanks to her pioneering work that soil analysis now has the same crime-fighting credibility as human DNA.

Lorna can extract information from samples the size of a grain of rice

Mud can be thought of as a slice of Battenberg cake in which layers of inorganic material, including base rock minerals and organic matter such as fallen leaves, twigs and vegetation, build up in identifiable components. This information acts like signatures, which can be read to reveal what was at the site yesterday, last week and as far back as 200 years ago.

A few years ago, scientists might only have been be able to say that someone had walked in an area the size of a square mile whereas today— thanks to Lorna’s work—it’s down to a few feet. In Scotland, scientists are using increasingly sophisticated technology to create virtual maps of the country’s 300,000 (and counting) different soil characteristics.     

As the UK’s leading expert on soil analysis, Lorna nearly always visits the burial sites she works on to see the lie of the land for herself. The lab work is meticulous because it needs to stand up to scrutiny in court. It’s been used to trap killers, rapists and terrorists who claim they’ve never been near the crime scene, when soil evidence on their footwear, clothing or vehicles proves the opposite.

"Sean had followed an old-fashioned policeman’s hunch that if the suspect had used the tools to dig Becky’s grave, then the mud on them might connect him to the scene"

One early spring morning three years ago, an officer on the other end of the phone was working on a cold case and he sounded exasperated. Detective Superintendant Sean Memory was pursuing Becky’s killer having seen her remains first hand, buried in Oxo Bottom field near Eastleach.

Halliwell had initially confessed to the killing and taken officers to the grave site himself but, due to a procedural technicality, the court had ruled his confession inadmissible, and Sean needed fresh evidence in order to link him to the crime. Lorna was his last hope of seeing justice done, as well as providing much-needed closure for Becky’s family.        

Halliwell was clearly going to be a challenge. Lorna arranged for soil samples to be taken from Becky’s grave, along with those from several gardening tools found at one of Halliwell’s old addresses, and sent to her laboratory at the James Hutton Institute in Aberdeen.

Soil analysis work is carried out on a shovel

“Sean had followed an old-fashioned policeman’s hunch that if the suspect had used the tools to dig Becky’s grave, then any mud on them might connect him to the scene,” Lorna explains.

Bizarrely, Halliwell’s old address, where he’d lived with his wife at the time of the murder, was just down the road from where he now lived with his current girlfriend.

Having gotten away with his crime for nearly a decade, he’d have been well aware that the net was closing in, even though he was behind bars for killing another Swindon girl, 22-year-old Sian O’Callaghan.

One of the biggest difficulties Lorna faced was that the samples from the spade, fork and pick axe were at least ten years old and most likely mixed with earth from more recent digging activity. “There was a high probability that Halliwell had used the tools after Becky’s body was found and I had to identify and separate out those materials to see what remained,” she says in a thick Scottish accent.      

There was an encouraging start in the lab when the scientist established that some of the soil could indeed date back to the time of Becky’s death. Over the last five years there have been significant advances in soil analysis, enabling fingerprint information to be obtained from a sample the size of a grain of rice. Not so long ago they’d have required a shovelful for the same results.

 “You have to follow every possible lead no matter how promising or how much of a red herring it may appear, because you never know which one might provide the vital piece of evidence”

The bid to catch Christopher Halliwell was code-named “Operation Manilla” and Lorna was busy dissecting and examining the granules lifted from his gardening tools under a high-magnification microscope. A piece of silver tape had also been discovered alongside Becky’s body and, while checking it for soil elements, she spotted a blue fibre and brown human hair attached to it, either of which could link Halliwell to Becky’s grave.

The two newly recovered items were sent for specialist testing but Lorna had been down too many blind alleys to assume success, and returned to the lab. “You have to follow every possible lead no matter how promising or how much of a red herring it may appear, because you never know which one might provide the vital piece of evidence,” she says.

Lorna has to keep an open mind about the suspect, who could be perfectly innocent, as well as any events which may have altered the chemical composition of the soil, such as a tool having been washed, or shoes splashed through a puddle. Interestingly, adding water to soil can sometimes help investigators because when it dries, tiny sticky aggregates can be locked-in.

Lorna’s interest in soil was sparked while growing up on her father’s potato farm

The scientist’s next job was to establish if the mineralogy, colour and texture of the samples from Halliwell’s tools matched those at Becky’s burial site and—although the initial results once again appeared positive—further analysis revealed that the resemblances extended way beyond the grave site. It demonstrated that Halliwell had been within the area, though nothing more. Further disappointment came when the test results on the fibre and hair proved inconclusive.

Lorna, whose interest in soil was sparked while growing up on her father’s potato farm in Angus County, south of Aberdeen, pressed on. She’d spent years developing a technique capable of scrutinising a soil’s minute organic content and decided to put it into practice.

“The organic aspect takes you to a much finer spatial scale of resolution,” she says, “or in other words, down to within feet and inches of where a suspect has been. Getting some sort of closure for the victims’ families is really rewarding and that’s what drives you on into the hard hours.”

After checking and double-checking, it was the moment Lorna and Sean had been hoping for. The miniscule aggregates from the yellowy-grey earth on the spade were almost indistinguishable in colour, texture, alcohol content and alkanes to that found at the edge of Becky’s grave. Both were also low in organic content and high in clay compounds—proving that in all likelihood Halliwell had dug her grave.

The taxi driver pleaded not guilty and declared that he wanted to defend himself. While in prison, he’d read every book he could get on forensic procedures and repeatedly challenged the scientist on whether she’d maintained the integrity of the exhibits, and properly wiped down benches between tests. One slip by Lorna could have derailed the whole case, but after Halliwell was sentenced to spend the rest of his life behind bars, the judge praised her clear and effective explanation of a complicated science. Becky’s mother also thanked her.

Detective Superintendent Sean Memory, who’s still actively investigating whether Christopher Halliwell might be responsible for even more murders and serious sexual offences, said, “Lorna’s evidence was absolutely critical in securing Christopher Halliwell’s conviction—she was our last throw of the dice. Soil analysis doesn’t have much of a history in British case law but, thanks to scientific advances, and hard work, that’s starting to change. Justice was finally done for Becky’s family.”

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