Solving crimes with geology
Image credit: Louise Murray
Geoforensics is a method the police and forensic scientists use to help solve murder-related crimes. Here we uncover cases where the innovative approach of analysing soil evidence proved successful.
Twenty-two series and 200 episodes of the BBC CSI drama ‘Silent Witness’ testifies to the enduring appeal of forensics in television. Real CSI (crime scene investigation) is somewhat different – less intuitive, more scientific, but just as fascinating, perhaps more so.
Forensic geology, also known as geoforensics, is the analysis of soil evidence to help solve crimes. Such evidence found at a crime scene can be definitively incriminating in the hands of experts.
Soil samples, from footwear or vehicle footwells, can demonstrate a clear timeline of the movements of suspects and their vehicles, making a lie of their stated alibi locations and tying them into a crime scene.
Mud recovered from a killer’s vehicle can direct a search for a missing body and help to secure a murder conviction, and geophysical techniques, commonly used in archaeology, can be deployed to reveal clandestine burials.
E&T meets three global experts in forensic geology who tease out the truth, through careful analysis of soil evidence, to identify criminals and find bodies.
Dr Pier Matteo Barone, an archaeologist and geoforensic expert based at the American University of Rome, was called in by police in central Italy in 2013, six months after the disappearance of an unnamed missing person. He was asked to check police intelligence to help to locate a body.
During the investigation, the police had two hypotheses. The first suggested that the body had been buried under a concrete road surface; this was easily disproved by checking timeline satellite imagery of the area to pinpoint when the road had been laid. Its construction post-dated the person’s disappearance. Other intelligence stated that the body had been buried in a nearby volcanic area known to contain many shallow subsurface caves.
In response to the hypotheses, Barone decided to use a ground-penetrating radar (GPR – see boxout below, Geophysics) to survey an area of almost one hectare with real-time results. The GPR was equipped with 500MHz antennas to create a radargram, and depth slices that showed the subsurface to about 3m below. It was possible to see a large cave about 2m underground and 3-4m in diameter. Something lay inside that needed investigation.
From hidden weapon caches to clandestine graves, geophysical search techniques can reveal secrets hidden under the soil or underwater. They can also augment or replace hugely expensive traditional searches, which are dependent on manpower resources to cover large areas of ground searching for signs of ground disturbance. As well as being expensive in terms of labour and time, these searches can be unproductive.
Ground-penetrating radar, or GPR, is commonly used in forensic search and often in conjunction with cadaver dogs to narrow down a search area. Up to four antennas of varying frequencies can be mounted on the device, which looks a little like a lawnmower on large wheels. On it, a mounted tablet shows the readout of the subsurface radargram to the operator in real time.
There is a trade-off between frequency and resolution: the higher the frequency the greater the resolution but the lower the depth of penetration. It is a technique used to search the subsurface, effective within a few metres from the ground surface.
Apart from its use in forensics, GPR is commonly used by utility companies to map underground pipes and cables, and other infrastructure.
ERT, or electrical resistivity tomography, is an electrical method deployed where GPR cannot function well, for instance in areas of high moisture or salt content. It is, however, much more time-consuming to set up and the results are not available to teams in real time.
Completing the geophysical toolbox, magnetometers are used to detect small variations in the Earth’s magnetic field. They can also be useful in forensic search applications to locate ferrous metallic objects such as a cache of weapons or a buried knife.
“GPR isn’t an X-ray device, but we could see an anomaly, something in a corner of the cave,” Barone explains. “I directed police to go around the hillside below, where they found an area of disturbed soil that had been dug over, and hidden under branches and bushes, concealing the entrance to a cave.”
After carefully removing the soil following archaeological excavation standards, layer by layer to preserve any evidence, it was clear that there was a partially decomposed body inside the cave. “Once forensic pathologists had a body to work with, that was obviously an enormous help to the police. The case has yet to go to trial, so I cannot be more specific with any other details,” says Barone.
In Northern Ireland in 2006, Queen’s University Belfast forensic geologist Alastair Ruffell was called into a complex double homicide case. Four brothers were accused of causing the deaths of a couple at their remote country cottage in South Armagh.
The couple had died in a conflagration following the explosion of combustible vapour inside their home; two of the suspects were also badly burned at the time and ended up in hospital in the Irish Republic. One brother had allegedly been abused by the deceased man some years previously. The four Smith brothers initially all had alibis for the evening in question.
“My first job was to collect and examine over 370 soil samples from the brothers’ homes, around the murder scene, and a quarry where one of four vehicles used had been dumped,” says Ruffell. “We were looking for key samples from footwear or cars that could tell the story of the movements of the owners in micro-stratigraphically layered soil deposits.
“I like to lay out my samples on a large white bench in a spatial distribution to represent the geography on the ground, and this helps me with an initial visual sorting of the samples,” Ruffell adds.
The soils analysed were mineral-rich, so Fourier transform infrared spectrophotometry (FTIR) measurements and an X-ray diffraction (XRD) were taken.
With FTIR, the sample was irradiated with infrared light so that the 3D structure of the molecules in the soil sample are revealed as a spectrograph. “The results from suspects’ boots or cars can then be compared to results from the known sampling sites,” Ruffell says.
XRD was used to categorise the mineral composition of the soil samples. Both techniques are non-destructive and served the purpose of helping to zoom in on the most helpful of samples, excluding others.
“Of the original 370 samples, we identified about 25 that from the chemical analysis of the soil from boots and vehicles, tell the story of where the suspects had been on that night, critically overturning their alibis, and directly linking them to the crime scene,” Ruffell concludes.
These samples were submitted for QemScan analysis, which uses energy-dispersive X-ray analysis of individual particles under the scanning electron microscope to map elemental contents and ratios of individual particles, further confirming the other results.
Moreover, two of the four cars owned by the brothers had superb evidence linking the vehicles to the track on the way into the scene of the crime and layered over that was the distinct geological signature of the quarry where one of the cars was dumped on the way out of the crime scene. These distinct layers also tied into samples taken from one of the men’s boots, conclusively disproving their alibis.
The four brothers were convicted of manslaughter after the jury accepted their version of events that there had been no intent to kill and were ultimately jailed for up to 11 years each.
Another case where geological evidence played a key role was the search for a missing person in northern England during 2013. On 7 March, Pamela Jackson’s sons reported their mother missing after not hearing from her for five days. Police quickly focused their attention on her partner, Adrian Muir, the last person to have seen her alive.
Muir was quickly established as the chief suspect after major inconsistencies appeared in his story of events as told to family members and to the police.
During the night and days after Jackson’s disappearance, mobile-phone tracking placed Muir in his car travelling between her home in County Durham and his home in Halifax. This tracking encompassed a huge area of the wild and isolated moors of West Yorkshire, and a distance of 100 miles by road. Muir was a fell runner and gamekeeper who knew the area well.
Given that there were no witnesses, a shallow grave could be dug in under five minutes in the soft peaty soil. Muir denied all involvement in the death of his partner, despite recording a suicide note on his phone shortly after her disappearance.
Professor Lorna Dawson, an eminent geoforensic scientist at the James Hutton Institute in Aberdeen, was called in by County Durham police as part of a specialist team from Alecto Forensic Services to assist in the search phase.
“We identified target-sampling sites across the search area supported by case-specific intelligence and recovered mud from a pair of gloves from the boot of Muir’s car,” Dawson analyses. “We also integrated models of body deposition behaviour such as convenient parking, soil diggability and seclusion from passers-by into our search strategy.”
They were able to exclude four out of the five possible search areas from their geology alone using an XRD mineralogical analysis of the soil. “That resulted in a theoretical area of approximately 5x3km2. Still large for a search area,” Dawson says.
The team turned to examining the organic composition of the soil from Muir’s gloves to narrow the search area further. Gas chromatographic analysis of the alcohol and alkane fractions of the soil organic material revealed specific information about the vegetation types at the site. Plant species can be identified from the waxy marker molecules on their surfaces.
These results allowed Dawson to direct the police to an area of moorland grass, distinct from the heather and gorse that covers much of the moors. Within that area, a police dog handler, Ian Jefferies, was able to use excellent field craft to identify the exact burial site, confirmed by his labrador Sid.
The results of the analysis of the mud on Muir’s gloves had taken police to where Pamela Jackson was found, but the team returned to Muir’s car to link him further to the actual burial site. Despite Muir’s best efforts to valet his car, they were able to retrieve a sample of soil aggregates deep in the pile of the footwell carpets. It matched the characteristics of the soil from the subsoil 60cm below the surface of the grave site, proving that he had been in contact with it.
Combined with other compelling evidence – such as Muir’s fingerprint on the cellophane of a bunch of flowers that he buried with his former partner, phone and CCTV records – a strong case brought together all the strands of evidence and led to Muir being sentenced to 18 years for the manslaughter of Pamela Jackson. To this day, Muir declares his innocence.
Geoforensic evidence in these three cases contributed to the locating of the bodies and, in two so far, the conviction of the killers.
All of the cases were complex and multifaceted. “The end result has to be justice for the victims and their families, bringing together of all the different strands of evidence to make a strong and compelling case to the court,” says Dawson.
Test beds for search techniques
How do you go about finding the best method to locate buried bodies? A good place to start is a body farm. The world’s first body farm was opened in 1971 at the University of Tennessee by Dr William Bass to study the process of decomposition of human bodies.
Bodies are buried clothed or unclothed in shallower or deeper graves, in different soil types, and at different times of year – all of which have a major effect on the speed of decomposition.
There are now six other body farms in the US, and new facilities have opened recently in Australia and the Netherlands.
Facilities in the UK use pigs as human corpse proxies. However, some scientists believe that pigs decompose quite differently from humans and so may be of limited use to science.
There is also huge variability in the speed of decomposition according to the geology. A body buried 50 or even 500 years ago in wet peat may still be almost intact, while a corpse buried in dry sand will rapidly decay.
Body farms have multiple purposes beyond the direct study of the mechanisms of human decomposition. Corpse or cadaver sniffer dogs can be trained at these sites, geophysicists can refine their choice of instrument, and the often difficult interpretation of the radargrams and depth slices that their instruments record. Police and forensic scientists can study and train in the best practice in evidence collection.
The problem with body farms is that even the oldest is not very old. So, researchers have looked at parts of old cemeteries that were being redeveloped to assist in replicating the circumstances of much older missing persons’ remains. This approach also has limitations as criminals generally do not use coffins in clandestine graves, but it is providing insight into how long bodies can be detected by geophysical methods, feeding into cold-case searches.
The facilities, varied as they are, depend on donations and by all accounts there is no shortage of these. It is thought that 120 people a year donate their bodies to the original Tennessee body farm.
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