The role of geoforensics in law enforcement and police investigations
Dr Laurance J Donnelly
Chair, The Geological Society of London, Forensic Geoscience Group (FGG)
International Union of Geological Sciences (IUGS), Geoscience for Environmental Management (GEM), Geoforensic International Network (GIN)
Geoforensics (known also as Forensic Geology or Forensic Geoscience) is the application of geology to criminal investigations. These may include for example; domestic incidents, international terrorism, humanitarian, environmental, geohazards, mining, geotechnical, civil engineering, materials engineering and fraudulent investigations.
Forensic geologists may assist the police, throughout the world, police to help investigate serious and high profile crimes, such as murder and rape. To help determine what happened,where and when it occurred, how and why a particular crime took place, or to locate graves or other buried or concealed objects.
At a recent meeting in Uruguay, South America, The International Union of Geological Sciences (IUGS), Commission on Geoscience for Environmental Management (GEM), established the Geoforensic International Network (GIN). This is an international working group on Geoforensics building on the success of the Geological Society of London Forensic Geoscience Group, established in 2006. These groups are aimed at promoting and developing the science of Geoforensics and promoting best practise.
In law enforcement context geoforensic specialist may support the police in two broad fields of geoforensics, geological (trace) evidence and search:
GEOLOGICAL (TRACE) EVIDENCE
This involves the collection, analysis, interpretation, presentation and explanation of geological evidence, which can be soils, sediments, rocks, micro-fossils or man-made materials (such as concrete, glass or bricks). These may be sampled from a crime scene, human remains (for example from skin or finger nail scrapings), vehicles, clothing or other objects. A forensic geologist may be able to assist the police in determining the possible location where a crime took place, linkage of the offender or evidence to a crime scene or victim, assess the possible movement of human remains, or eliminate potential suspects or offenders. These types of ‘geological’ samples are analysed in a laboratory and it is important they are properly collected by the forensic geologist from the crime scene, object, or body.
Geological evidence is based on the principal that when two objects make contact there is transfer of material from one object to the other. The transfer may be short-lived, or beyond detection, but nevertheless the transfer has taken place (known as the Locard Principle, 1929). The geological evidence may then be used to see if there could be an association between different items or objects. For example, does the soil in the footwell of a vehicle or on the shoes of a suspect originated from contact with soil exposed at a crime scene?
History & background. The first application of geology to help the police investigate crime is not known with any degree of certainty. In Christian Ehrenberg (1795-1896), working in Belgium, analysed microfossils found in sand to assist the police with their inquires during a substitution case when silver had been stolen and replaced by the sand. In the late 1800s and early 1900s, Sir Arthur Conan Doyle’s fictitious Sherlock Homes character, was able to tell which part of London Dr Watson had been walking due to the colour and consistency of clay (mud) splashes on the bottom of his trousers. It was the invention of the microscope which greatly assisted in enabling minerals and soils to be identified on suspects clothing. In the late 1800 and early 1900s some crimes in Europe were brought to successful prosecution as the mineralogical analysis of soil and rock fragments were able to show an association between an offender/suspect and victim.
Collection. Geological trace evidence can vary considerably and may include for example rock fragments, soils and sediments, which occur naturally in the ground, artificial (anthropogenic) man-made materials derived from geological raw materials (such as bricks, concrete, glass or plaster board), or micro-fossils. These may be transferred onto the body or clothing of a victim or offender at the crime scene. The huge variability of rocks and soils, particularly in the United Kingdom, is helpful in potentially placing an offender or item at a particular location. Geologists are trained in the principles of stratigraphy and the laws of superposition. In simple terms, younger sediments (and soils) are deposited on top of older ones and cross cutting relationships may be used to identify the order of soil deposition. This relationship for example may be observed on a shoe where layers of different soils could help to explain where and when an offender may have been present at a particular place. Micro samples for example on clothing, below finger nails, on tools in vehicles may require the development of careful and innovative sampling techniques to recover the samples. Due consideration must be given to the labelling, transportation, storage of soil samples with an appropriate chain of custody that must be rigorously maintained at all times so the history of the samples can be traced. The collection of soil samples must always be undertaken by, or supervised by a trained forensics geologist.
Analytical strategy. There are a wide variety of techniques for the analysis of geological materials. The types of tests conducted will depend on several factors such as; what questions are being asked (eg. “Are the two samples similar?” Or, “Where did the sample come from?”), equipment availability, time frames involved, cost, resources and finance/budgets to fund the analysis, type of sample, size and volume of sample. Ideally the types of analysis should be non-destructive to allow repeatability if necessary. The analysis will aim to describe, identify, classify and identify the materials. Typical analysis may include a determination of; (a) its physical properties (eg. colour, texture, particle size, shape and morphology), (b) chemical properties (eg. elemental chemical composition, volatile compounds, Eh, Ph, stable or radiometric isotopes), (c) mineralogy may be analysed from a thin section, scanning electron microscope, x ray diffraction, Raman spectroscopy, electron microprobe or automated mineral analysis (eg. Qemscan), (d) biological components (eg. pollen, micro flora, microfauma, mycology, microbiology.
Evaluation. An evaluation will be conducted to determine if there is an association between the soil samples and/or rock fragments collected from the items/objects belonging to the suspect and samples collected from the crime scene. Careful consideration will be required during the evaluation of analytical data. For instance, are the small size of the samples collected actually a true representation of the crime scene? Do soil samples adhere to certain types of materials than others? If the two mineralogical samples are identical these can not confirm whether they originated from the sample place, as there may be another unknown location which has the same mineralogy. This may however provide strong circumstantial evidence which could be supportive of other evidence in a case. An identical mineralogical association may be determined if however, two samples of a broken object (such as rock, brick, tile, or other man made object) are being compared. The geological analysis of items and objects can be used to exclude them from an enquiry.
Reporting of results and communication. Geological evidence may be presented in court by a prosecution team and will be open to challenge. This therefore means that strict protocols must be followed during the sampling, analysis, interpretation, reporting, presentation and communication of geological evidence. The forensic geologist will have a duty to report the results to the court in a clear, fair, unbiased and impartial manner, be this verbally or written. Police officers are likely to have a limited knowledge of geology, but most have the ability to learn quickly. The jury, accused, prosecution, lawyers, barristers, judge, press, media and public will have varying levels of geological knowledge and the communication of geological information often is the most difficult part of an investigation.
Geologists are trained in the mapping and exploration of the Earth’s (ground) surface, for example; to investigate geological hazards, mineral exploration or to determine the ground conditions for the citing of an engineered structure.
Geological techniques may be used to help the police search for locating (and sometimes the recovery of) buried or concealed organic remains (such as a murder victim’s graves, mass graves and human remains) or non-organic objects (such as clothing, weapons, firearms, improvised devises, explosives, drugs, stolen items, money, jewellery and antiques). These searches may take place in urban, rural and remote locations, in both the terrestrial (land) and marine (including also underwater such as canals, rivers, streams, seas, lagoons, estuaries, reservoirs, lakes and ponds) environments.
What is a search? A search is the application & management of systematic procedures, combined with appropriate detection equipment to locate specified targets (or object). It is the skill of looking for a specific object & the art of finding it.
What is the aim of a search? A search may be conducted to; (a) obtain evidence for prosecution, (b) gain intelligence, (c) deprive criminals of their resources & opportunities, (d) locate vulnerable persons, (e) protect potential targets, (f) search for homicide graves & associated buried items or objects.
History & development of search. Historically, police methods of finding murder victim’s graves often involved large-scale gridded areas with personnel ‘finger-tip/line searches’ and ‘trial-and-error’ excavations. These may be inefficient, labour intensive, may destroy evidence and ignore subtle ground disturbances possibly related to a burial. They may be supported by non-specialists, such as public volunteers and local interest groups. However, the effectiveness of large numbers of public volunteers, or military infantry forming large lines and walking through large gridded areas of open land or woodland, must be considered with respect to whether such groups will successfully locate a highly concealed sub-surface burial. Following the Provisional IRA efforts to ‘blow-up’ the British cabinet in the Grand Hotel, Brighton, in 1984, the police started to become more familiar in conventional search techniques by undertaking training with the British military. At this time the military had experience in ‘search’ to, for example, help locate terrorist devices. The subsequent establishment of the Police National Search Centre provided formal training for police officers which included PolSA (Police Search Advisor) accreditation. Most forces in the UK now have at least one fully qualified PolSA.
What are the types of search? An offensive search is used to locate a specific item sought obtain evidence or to restrict an individual’s room to manoeuvre & their operation. Adefensive search is used to maintain freedom of action & movement for the public.
What are the types of search? These include; (a) person search, (b) missing person search, (c) building searches, (d) vehicle searches, (e) motorway & road searches, (f) mass fatality searches, (g) search ‘for’ and ‘of’ crime scene searches (water & land based). Geologists mainly will be involved with the latter.
Search philosophy. (a) In order to find a grave we must first understand what we are looking for? (b) The search for a grave is a pragmatic balance between a minimum acceptable standard & minimal expenditure. (c) It is the search for rather than of a crime scene.
Search considerations. (a) What are the choices of search assets, (b) what is the equipment availability and limiting factors, (c) what are the financial, logistical and technical constraints, (d) is the search measurable, cost-effective & proportionate, (e) can the search achive a minimum standard resolution for a high probability of success, (f) what is the exit strategy?
What are the external factors that may influence a search? (a) weather conditions, (b) type of terrain, (c) press & media, (d) psychics, (e) the public & communities, (f) victims family members & friends, (g) time frames involved (h) search area (i) whether the search is covert or overt.
What are the different search categories?
- Search and rescue. The person is lost and active in their self discovery. This is based on ‘area searching’ and the assumption that a person, or persons, will travel a maximum given distance within a set time, if mobile. These searches may cover geographically large areas. The search is subjective and based on assumed actions of missing or lost persons.
- Scenario based. This uses behavioural profiling of the offender(s), geographical profiling and victimology assessment so the victim. It requires the investigator to generate a hypothesis. There is no correlation of distance with time. The search is objective and is based on known facts and the victim’s last movements.
- Feature based. Based on the identification of primary, secondary and tertiary physical (geological) markers which may have been consciously or sub-consciously used by the offender to locate the grave site. In other words this involved decoding the offender’s modus operandi?
- Intelligence led. All law enforcement searches should be intelligence led based on facts and intelligence that enables a hypothesis to be generated.
- Systematic Operational Procedure. A SOP should be applied to all searches. This provides an assurance of search consistency and enables peer and independent reviews. This should be in written format and forms part of the search documentation.
Predictive models. Databases and 'models' may facilitate a search and include for example; offender profiling or geographic profiling, missing person, suicide, weapon, drug concealment & body deposition models.
Offender behavioural characteristics. Offenders who dispose of victims may consider:
- The principal of least effort. That is, choose the easiest option to dig a grave.
- ‘We go where we know’. Choose a location he/she is familiar with, previously visited by the offender so he/she can; (a) have an explanation for his/her presence if disturbed or arrested, (b) facilitate ease of access and egress, (c) can find his/her way in darkness, (d) contains familiar landmark features.
- Concealment. (a) low witness potential, (b) act of concealment/burial is under cover.
The Conceptual Geological Model for a Grave. As a completely concealed burial takes place in the ground a reconnaissance visit to the crime scene/search area must be conducted, by the forensic geologist & law enforcement officer, so a conceptual geological model may be developed. This will enable an estimation of the graves conditions and this in turn will pre-determine the most likely choice of search assets to locate the grave. A conceptual model of a potential burial site gives an estimate of what is likely to be found and the condition of the target. Conceptual geological models are developed at the beginning of a search. It is a model to be tested, revised and tested again until it can be verified (at discovery) or proven otherwise and therefore abandoned. A conceptual model is often based on the individual geologist’s experience from conducting geological investigations in comparable geological settings. High quality geological information (such as published geological maps, memoirs, papers and technical reports) will support a search effort with a high level of assurance, but a weak geological model for the grave site will introduce uncertainty into the search, now matter how precise and accurate the subsequent exploration (search) techniques. The development of a geological model for a victim of homicide, or a grave, requires a specific understanding of the natural (geological) ground conditions and how these have been influenced by the activities of the offender (e.g. digging, and subsequent reinstatement of the disturbed ground). At any one location there are likely to be a number of interactive, dynamic, active surface geological processes, which have affected the rocks, soil, groundwater and topography. These processes were active long before burial took place and are likely to have continued in the time which has passed since. No single geological model suits all types of search areas and there is no single approach to producing a geological model, as each homicide case and search area will have unique characteristics. This is one of the primary roles for the geoscientist, which will vary from case to case. The most valuable contribution a geologist can give a law enforcement (police) officer (or search strategist), is to ‘get the geology right’!
Geological factors. The development of a conceptual geological model must consider; (a) the geological setting, (b) hydrology & hydrogeology (groundwater), (c) principal soil types & superficial deposits, (d) nature of the bedrock interface, (e) principal lithologies, (f) engineering and physical properties of the underlying strata (rocks), (g) mineralogy, (h) geological structure, (i) ancient & active geomorphological processes which may have changed the grave since it was originally dug, (j) past & current land use, (k) geological hazards, (l) weathering & erosion, (m) preservations & decomposition of human remains, (n) weather and local climate.
Anthropogenic (man’s) influences. Man’s activities may also influence the search for a grave as these can change the ground conditions and include for example; mining, construction, building works, waste disposal or farming.
Digability & excavatability surveys. Body disposal mainly takes place in soil, superficial deposits, or softer rocks (such as some shales and mud rocks). The ease of which the soil can be dug (ie. its digability) and placed back into grave (or reinstated) is of critical importance. The offender is likely to choose a site where the soil is sufficiently thick, and can be quickly dug then reinstated, preferably with no or little surface indication that digging has taken. The digability of soil depends on its geological properties such as; (a) intact strength, (b) bulk density, (c) groundwater regime, (d) depth, (e) weathering, (f) proximity of the underlying bedrock interface, (g) slope angle, (h) vegetation cover, (i) stability of the walls upon excavation, (j) bulking and swelling of the soil and (k) the method of digging and choice of digging implements. There is no generally accepted quantitative measure of digability. This can only be determined by in situ ‘trial and error’ testing. In situ digability tests may be easily performed, before the main phase of the detailed survey (usually at the reconnaissance stage), involving either probing or digging using tools similar to those to which the offender is believed to have had access. This also provides the opportunity to inspect the soil structure and/or weathered bedrock and associated superficial deposits to determine whether it is granular (sand rich), cohesive (clay rich) or organic (peat). These observations are important as they have critical implications on the efficiency of burial and the preservation or decomposition of human remains depending on the time elapsed since burial. A digability survey will; (a) provide geological information on the soil processes, groundwater and rock types, (b) demonstrate the level of difficulty or ease, and time required, for a shallow grave to be dug, and the effective depth which can be achieved, (c) demonstrate how effectively the soil can be reinstated and what visible topographical features may exist, to indicate the possible presence of the grave and (d) provide a prediction of the length of time it would take an offender to dispose of the body.
What is being searched for? Objects or items associated with the victim’s body shodul be considered as these may increase the probabilities of locating the grave. These may include for example; (a) weapons like firearms or a knife possibly used during the murder, (b) clothing containing ferrous or non-ferrous metal components such as zips, studs and buckles, (c) drugs, (d) money & coinage, (e) leachate plumes associated with decomposition and skeletonisation of human remains, (f) gas/odours/scent being emitted from decomposition of human remains and (g) is there a grave cut (ie. the boundary or contact between disturbed and insitu geology)?
Geological search assets, methods and techniques. Geological exploration and prospecting methods conventionally used to explore the ground in mineral exploration and geotechnical site investigations are adaptable and applicable to searches for homicide graves. The type of survey, methodology and interpretation of data acquired depends upon several complex factors including; (a) types of target buried (such as human remains, money, explosives, weapons); (b) geological conditions, (c) anticipated depth of burial, (d) age of burial and (e) experience and skill of the individual geoscientist(s). Geological surveys can be carried out by one person, or a team, they may be non-invasive or invasive. They are usually conducted from the macro-scale (cover many tens of square metres) to the micro-scale (covering just a few square metres of ground) and may take hours to weeks (sometimes years) to complete. Typical geological assets and methods which may be used to search for a grave may include for example:
- Remote sensing. There is now available a variety of remote sensing techniques that may facilitate with the search for a grave. Where large complex data sets are obtained they may be managed and analysed using spatial location and geographic information systems (GIS) and geostatistics. Typical and remote sensing methods include for example; (a) infrared photography, (b) elevation modelling, (c) satellite modelling, (d) hyperspectral and multispectral imaging, (e) laser scanning, (f) long distance LiDAR, (g) Synthetic Aperture Radar (SAR) & interferometry, (h) X-ray imagery & tomography, (i) neutron activation, (j) field portable x-ray fluorescence and (k) thermal imagery.
- Analysis of high resolution air photographs. Conventional aerial photography (vertical & oblique) may often be used in association with geological mapping. This may be particularly useful if the photographs are taken as stereo pairs to exaggerate any ground disturbances.
- Ground based geological & geomorphological mapping. This may enable ground disturbances to be identified, analysed and interpreted as being associated with natural geological processes, the activities of man (such as mining and construction) or digging.
- Geophysics. Geophysical investigations rarely require any contact with the ground surface (i.e. they are non-invasive) for their operation and therefore adhere to the law enforcement preference of moving proportionately from the non-invasive to the invasive in forensic searches, thus minimising evidential contamination and damage to crime scenes. The data obtained provides measures of the vertical and lateral variation of the physical properties of the ground. These data can only be interpreted in the light of knowledge of the likely ground conditions, from the conceptual geological model. Typical geophysical techniques that may be suitable to search for graves may include; (a) magnetic, (b) resistivity, (c) induced polarisation, (d) self potential, (e) electromagnetic (conductivity), (f) ground penetrating radar (GPR), (g) metal detectors, (h) seismic, (i) microgravity, (j) air borne geophysical surveys, (k) geophysical exploration platforms (multiple geophysical sensors which may be simultaneous deployed to provide a faster and more effective way to survey large areas of land, usually towed behind a 4x4 vehicle or tractor).
- Hydrochemistry & geochemistry. An understanding of the hydrogeology in the vicinity of a grave site is necessary as it influences; (a) surface flow paths and run-off (b) groundwater flows, (c) decomposition or preservation of human remains (d) generation of leachate plumes from decomposing human remains, (e) migration of body scent (gas/vapour) and (f) the deployment of the most suitable non-invasive geophysical and geochemical techniques. Leachate plumes may also increase the aerial footprint of geochemical and geophysical signatures and therefore enhance the possibility for detection. The direction and distance of the plume will depend on several factors such as ground permeability, geological structures, lithology, rainfall and time elapsed since burial. By comparison with exploration geophysical methods, hydrochemical and geochemical search techniques are less well developed. Carbon-13 and strontium-87 isotope analysis of bone or teeth respectively may also be used to identify the geographic provenance of human remains.
- Geological analysis of police intelligence. Written statements, crime scene photographs and body disposal plans, when analysed from a geological perspective may provide information to assist with a search.
- Probing. Soil probes when used during a ‘line search’ at close spacing are an effective means to search for a grave.
- Trenching. Hand held digging implements (such as spades, picks and mattocks) may be used to dig exploratory ‘trial pits’ or ‘inspection pits’, often to verify a geophysical anomaly or positive dog indication.
- Police dogs. Often known as ‘cadaver dogs’, ‘victim recovery dogs (VRD), or ‘human remains dogs (HRD)’ are an essential assets for any search and are reliable in most, but not all, geological conditions. The science which underpins the deployment of police dogs is not yet fully understood or explainable.
Communication between forensic geologists’ and the Police. Searches for graves may involve teams of multi-disciplinary experts such as; geologists, anthropologists, botanists, victim recovery dog handlers, remote sensing aerial assets, behavioural profilers, clinical psychologists and the military personnel. These searches are usually co-ordinated and managed by a Senior Investigating Officer (SIO), Police Search Adviser (POLSA) or search strategist. To successfully carry out the above search, the main challenges are not technical but communication. The forensic geologist conveys all of the above technical information to the SIO and other experts. The police officer may have already a team of multi-disciplinary technical, subject matter specialists. How does the geologist fit into this system? At what stage does the geologist approach the crime scene to reduce the risks of any cross contamination? How can the geologist begin to understand crime scene management and crime scene investigation and what are the strict police protocols involved? The SIO, already possibly over-loaded with a range of specialists, now finds that he/she has to deal with yet another specialist, the geologist. This may potentially be problematic if the process is not carefully planned and communicated.