Diatom analysis, as a forensic investigation technique, is a fairly niche tool. It has many applications in forensic investigations, such as direct environmental analysis in soil and water samples, alongside being present in human tissue, hair, and material adhesion. This particular form of evidence evaluation sees species identification merge with ecological interpretation.
Forensic ecology is about understanding and using different elements of a landscape to try and build a picture of what a landscape looks like for major crime and body deposition. However, it can also be used to evaluate how potential suspects move in a landscape, and considers how different variables can form part of the examination and exhibits process for major crime investigation.
What are the applications of diatom analysis?
One of the things that ecologists are very interested in, particularly with suspect movement, is understanding how likely it is that somebody has visited an area that isn’t akin with their usual behaviour. For example, this could present itself as why someone from a very urban environment, who isn’t known to walk in a woodland, suddenly has different items on their shoes and clothing that suggests they have been moving in a specific or local woodland.
When we look at exhibits such as hair, clothing, human tissue, vehicles and bags, the principle examination process is to look for either soil, vegetation, or water that may contain different diagnostics (i.e. diatoms), and can thus can build a bigger picture of where those elements have come from.
For example, in soils, we can characterise the inorganic elements by looking at its components, such as structures, colour and texture. This enables us to see whether the soil is local to a given environment. Alternatively, we can look at the organic part and consider the preservation of different diagnostic variables that can be used to reconstruct an environment, such as diatoms and pollen grains. We also look at clothing, shoes, and vehicle tapings for diatom analysis.
How do diatoms fit within the forensic ecology input?
Heritage crime investigation involves looking at soils, characterising the soils, and determining how the organic and inorganic elements can be linked to a specific environment.
What we try to do in terms of building a strategy for input is scene attendance. It is useful because we can take diatom samples and try to understand a landscape. However, we also like to go to briefings to provide input into a broader forensic strategy. We occasionally carry out joint examinations with biologists, because the work that we do can sometimes be quite disruptive, such as taking soils off clothing. If there are more important concerns, such as DNA or blood, we will go and do joint examinations with biologists so they can do their work first and we can then carry out ours afterwards, to ensure that we are not destroying evidence for other scientists.
What are the questions that need addressing with forensic analysis involving diatoms?
Diatoms are particularly useful due to their hardy nature, which is owing to the fact that they can survive in the environment due to their strong silica exterior.
With regards to soils adhering to car tyres and car footwells, our focus would be on the diatoms located in the soils. The access point and the location are looked at when you’re attending a scene and trying to capture soils to build up a bigger picture of that scene. For example, if a body is deposited in a woodland, this would involve identifying the different soils that could characterise that woodland, and then assessing whether we could use those to in relation to soils on a suspect’s footwear. This analysis would enable us to look at potential access points and how they’ve come into a scene, and perhaps can provide more of a narrative of the body deposition process.
With body deposition, we can certainly use these kind of skillsets within forensic ecology and reconnaissance for wider discussions with the police on potential strategies for finding a body.
Water Courses: A case for sampling
The Google Earth image above is from a water course which is very complex, in the sense that it’s marine, an estuarine and a riverine system. In terms of sampling, it’s quite difficult to capture the right samples to represent those different environments.
The photograph above can be used to demonstrate sampling points that we would take to try and capture the environments. It’s important to note that we do find different types of diatoms in different environments. There are several different variables affecting diatom species, such as:
- River flow
- Amount of organic content
- Different environments for them to cling onto
For example, on the right-hand side of the image there’s a more built-up area, so there may be more stones for the diatoms to live on.
Vehicle Tapings and Soil Comparisons
Vehicle tapings are quite difficult to look at under the microscope. In this case, the police didn’t have any ecology input and then it was asked for by the Crown Prosecution Service (CPS). The CPS asked to look at the vehicle tapings and we were very lucky in terms of what they uncovered. Tapings are a good way to get an initial overview of potential ecology strategies, as you can have a look and see what’s there, and ultimately decide whether or not it’s worth any further investigation.
That’s something that we’re really keen to push with diatoms work – using existing toolkits within a Crime Scene Investigator (CSI’s) work that we can use for diatom analysis. Instead of creating additional exhibits, this would involve using those that exist already within a CSI’s toolkit.
Landscape Characterisation and Scales of Landscape
The idea of characterising the local and regional landscape environment goes back to the idea of suspect movement. The local environment is more direct about the scenes. For example, if you have a body in a woodland, we would typically consider:
- What the environment around the body looks like
- Is the environment distinct from the regional area (within 200-300 metres)?
- Is there a change of woodland that steps into a grassland?
- Is there a woodland that steps out onto an urban area?
- Are there different ecological indicators that can demonstrate suspect movement from the regional environment to the local environment around the body?
If we’re just looking at soils in general, we like to get an overall picture of what the ecological assemblage looks like. This involves considering what kind of soils are present, are there any diatoms present, and is there potential for further vegetation work. Effectively, this is about getting an overview. If we’re not looking specifically for diatoms, then we will try to characterise that whole environmental picture.
Alecto Forensics is a UK leading forensic ecology service provider, delivering specialist forensic services and expertise to police forces across the UK.
We have over twenty years of forensic ecology experience within major crime investigation and pride ourselves on being an independent, quality-driven forensic service provider. We have a host of accredited experts and our expertise is available 24 hours 7 days a week.
We offer a full provision of service, from initial advice and support to scene deployment, laboratory analysis and final reporting.