What is Trace Evidence and how can it be analysed?
Trace evidence today:
Sadly, trace evidence analysis today is often underappreciated, underestimated and, crucially, underfunded. Having been severely impacted by budget cuts over the past 15-20 years, the discipline is worryingly close to extinction in many laboratories. Despite recent trends towards prioritizing DNA and digital forensics, the value of trace evidence has not diminished and the discipline retains huge potential for solving criminal cases, with trace evidence often being paramount in proving connections between victims, crime scenes, and suspects, in ways that disciplines such as DNA, digital forensics, or fingerprints cannot always achieve.
During a recent seminar at forster+freeman HQ, forensic scientist Bob Green OBE, poignantly stated that “there’s a cost to new tech, but what is the cost of not solving crimes?”, underscoring the importance of investment in all areas of forensic science which have the potential to deliver justice, regardless of trends. The alarming trend of neglect towards trace evidence should be challenged, and the critical need for increased investment recognised: after all, we don’t have to look further than a quick web search to find numerous examples of the indispensable contributions trace evidence has made to the justice system.
Bob Green OBE during his ‘Forensic Science at it’s Best’ presentation. While not specifically focused on trace evidence, Bob made some interesting points with relevance to the wider forensic science landscape today.
This article will delve deeper into the fascinating world of trace evidence, exploring its significance, the diverse analytical techniques employed, and the critical need for continued investment in this vital area of forensic science.
We will also consider how foster+freeman technology can offer examiners a multitude of examination techniques at a good price-performance value ratio, providing crucial tools while combating the challenges posed by limited funding.
A deeper understanding:
Often considered the father of forensic science, Edmond Locard suggested in his Exchange Principle that “every contact leaves a trace”, meaning that whenever two objects come into contact, there is an exchange of materials, no matter how difficult to perceive. This theory suggests that small pieces of material will be transferred from one person, place, or object to another, where they wait to be discovered.
Despite their diminutive size, small pieces of trace evidence may often have significant forensic potential and influence on a case, with even microscopic fragments holding the potential to reveal interactions, movements, and associations that would otherwise be unknown or unprovable: placing a suspect at a crime scene, confirming a victim’s presence, or revealing contact with certain objects, which can help to prove or disprove an individual’s stated series of events.
The evolution of forensic science technology has served to support Locard’s principle, as modern equipment enables examiners to detect trace evidence which would previously have been barely perceptible or invisible to the naked eye.
Image of Locard by Unbekannt >100 Jahre – Minerva: Jahrbuch der gelehrten Welt, Band 18, W. de Gruyter, 1916, Public Domain
Trace evidence analysis:
key methods and technology
We now delve into the sophisticated methods and technology employed by forensic scientists to analyse trace evidence, exploring 6 key methods and considering the unique advantages of each while showcasing the foster+freeman ffTA system – a powerful instrument equipped with modules dedicated to each of the following techniques.
Glass Refractive Index Measurement (GRIM)
Glass Refractive Index Measurement (GRIM) is a powerful forensic technique used to identify and group glass fragments based on their unique refractive indices, a key optical property that varies between different types of glass. GRIM allows investigators to determine if separate fragments originated from the same source, which can have huge forensic value in linking victims, suspects, and crime scenes, particularly for crimes involving break-ins or vehicles.
The foster+freeman ffTA GRIM 3 module determines the refractive indices of glass through the laboratory standard process of immersing a glass fragment in oil on a heated stage and precisely raising the temperature until the fragment disappears from view, indicating a refractive index match between the glass and the oil, for which the refractive index is known.
foster+freeman revolutionized this previously labour-intensive technique, and in doing so clearly defined the GRIM module as as the industry standard. The module has evolved since it’s release, with the latest GRIM 3 module streamlining casework by monitoring up to four glass fragment edges simultaneously, significantly improving statistical accuracy, reducing calibration time, and accelerating the examination process.
ABOVE: Join foster+freeman CEO Bob Dartnell for a GRIM Tale
Multi-wavelength Raman spectroscopy
Raman spectroscopy is a highly versatile trace evidence analysis technique used to compare numerous samples and, with the aid of spectra databases, identify materials. This powerful analytical tool is widely used in forensic science for the study of a variety of organic and inorganic materials including paint chips, fibres, inks, controlled substances, precursors, pesticides, and residues from explosives, flammables, and accelerants.
The technique is based on the Raman scattering effect that occurs when a material is exposed to certain wavelengths of light. Forensic scientists use the resulting spectra to determine a molecule’s structure, producing a unique “fingerprint” for comparison against other materials. Key benefits of Raman spectroscopy include non-contact, non-destructive analysis, analysis of materials in solid or liquid form, and rapid examination with minimal preparation.
The foster+freeman Foram X3 module for the ffTA system is equipped with a choice of laser wavelengths – 785 nm (invisible), 640 nm, and 532 nm – making it a uniquely versatile Raman spectroscopy device. The 532nm laser offers high sensitivity, the 785nm infrared laser suppresses fluorescence, and the 638nm laser provides a balance between power and sensitivity. Raman databases are also provided for the Foram X3 to aid in identifying substances such as paints, drugs, and accelerants.
VIDEOS: Join foster+freeman product specialists Justin Gould and Dan Freeman for an overview of the Raman process and Foram3 system for the ffTA.
Polarised Light Microscopy
Polarised Light Microscopy (PLM) is a widely used microscopy technique in forensic science, which is valuable for detecting, identifying, and analysing small unknown particles. The technique is known to be particularly effective in identifying fibres, minerals, chemical crystals, and rocks. A contrast-enhancing technique, PLM uses the birefringent properties of materials to improve image quality. Light becomes polarized when passed through a polarizing filter, orienting all light waves in the same direction.
PLMs are particularly useful in analysing fibres and minerals because they can determine specific optical properties, such as refractive indices and birefringence, which aid in material identification. Birefringence, the decomposition of a single light ray into two as it passes through birefringent materials, allows for identification of unknown materials against an interference colour chart by measuring sample diameter and the colour retardation of the decomposed light.
The foster+freeman ffTA system offers a PLM module consisting of a linear polarizer on the condenser lens, a second polarizer (the analyser) in the optical pathway before the observation tubes and camera, and a retardation plate to enhance optical path differences between the cross-polarizers.
Specimens are placed on a 360-degree circular rotating specimen stage equipped with two Vernier scales for rotation angle measurements to an accuracy of 0.1 degree. The addition of this rotating stage enables accurate measurements of a sample’s birefringence and quick identification of fibres such as acetate, acrylic, nylon, or polyester.
Fluorescence imaging
With wide ranging applications in the forensic laboratory, fluorescence imaging is an ideal technique for the inspection of biological samples, examination of accelerants (petrol, diesel, kerosene etc.), and for the characterisation and identification of illegal substances. In addition to visual inspection, fluorescence microspectrometry is a powerful technique for the discrimination of textile fibres and for the comparison of paint evidence.
The foster+freeman ffTA Fluorescence Imaging Module allows examiners to use UV, violet, blue, and green wavelengths to excite fluorescence in trace evidence and undertake examinations in real-time. High resolution fluorescence imaging and spectra is enhanced when used in conjunction with the ffTATM Micro-spectrometer module.
UV-Vis-IR Microspectrometry
Microspectrometry is a powerful analytical tool that is widely used in forensic science for the study and comparison of trace materials including paint chips, fibres and inks, being particularly effective in the discrimination of fibres that may have identical physical properties. Spectra in the visible region provide the user with objective measurements of colour, and through the examination of ultra-violet and infra-red spectra, users are able to make comparisons between two materials that may be indistinguishable to the naked eye.
The foster+freeman ffTA Microspectrometer module is available in a choice of wavelength ranges. Depending on the wavelength range selected, the microspectrometer will record absorption, reflection, and transmission spectra in the UV, Visible or Infrared wavebands. When used in conjunction with the ffTA Fluorescence Imaging module, it is also capable of recording fluorescence spectra.
VIDEO: Join foster+freeman product specialist Justin Gould as he domenstrates using the ffTA UV-Vis-IR microspectrometer module to examine hairs and fibres. The video also includes information on the annotation features of the VSC-style imaging suite.
Image Processing
The analysis of almost any item of trace evidence begins with a visual examination, to assess physical characteristics and make crucial decisions about how to proceed with any further analysis. This initial step is vital to laboratory workflow and the ultimate forensic value produced, and experts rely on modern tools and technology to process images at this stage more effectively and efficiently.
The foster+freeman ffTA is available with a comprehensive module for processing images, comprising a high resolution, scientific-grade 5 million pixel CCD colour camera, and powerful software, which are seamlessly integrated to enable the examiner to zoom, orientate and position items of evidence on screen for critical visual examination.
The software boasts a comprehensive suite of image enhancement and processing tools, including contrast stretching, HSL and RGB adjustments, equalization, FFT, and gamma correction. For image analysis, calibrated grids are provided to facilitate precise measurements of distance, angle, and area, with the option to add these measurements directly to the image, with further annotation supported by editable text and shapes.
Robust image comparison and transformation tools allow for side-by-side comparison of live and stored images with user-adjustable split position, superimposition, and subtraction capabilities (including red/green rendering), and the ability to rotate both live and stored images in 90-degree increments.
Challenges, Solutions, and Conclusions
As we have discussed, trace evidence encompasses a diverse array of materials that may have been transferred between individuals, objects, and locations during criminal activities. Extracting meaningful information from these often minuscule samples presents a number of challenges which must be addressed in order to unlock the wider potential of trace evidence analysis in the current landscape.
The foster+freeman ffTA, our flagship trace evidence examination system, aims to address these challenges by exemplifying a modern, modular approach to trace evidence analysis. Here we consider 3 key challenges and how the ffTA is designed to combat them:
Challenge
The effectiveness of all trace evidence analysis relies upon highly skilled and experienced examiners. Despite advancements in technology increasing the scope, accessibility, and efficiency of trace evidence analysis, a high level of expertise and solid forensic understanding is required to undertake many analysis processes and produce meaningful, court-ready evidence.
As such, trace evidence examiners are a commodity in themselves, with staffing, budgets, and time restraints often dictating evidence throughput in a laboratory, and the depth and breadth of the analysis that takes place.
Solution
The ffTA system is designed to maximise the expertise of the examiner and extract the maximum amount of forensic evidence in the shortest possible time, with the unique modular design utilizing an optical multiplexer to allow the operator to seamlessly switch between 6 available modules to perform a wide range of analytical tasks.
This increase in efficiency enhances evidence throughput, allowing labs to gain maximum forensic value from their key resource: the examiner.
Challenge
Many trace evidence analysis processes require advanced and complex single-purpose devices, which can often be prohibitively expensive for forensic laboratories dealing with tight budget constraints, and be seen to represent a poor price-performance value ratio.
Solution
An innovative ‘multi-examination system’, the ffTA is a versatile and cost-effective solution for laboratories, removing the need for multiple expensive devices while empowering examiners with a wide range of analytical capabilities on a single platform. Value is further enhanced by the modular design, reducing the initial cost while also providing the flexibility to bolt-on additional functionality as the need, or funding to do so, becomes apparent or available.
Challenge
Further challenges arise as forensic scientists prioritize the integrity of their evidence, often making destructive or invasive analytical methods a last resort.
Solution
Each of the 6 ffTA modules is non-destructive to ensure the integrity of evidence is preserved and maximum forensic value can be achieved by subjecting samples to a range of analytical techniques
Conclusions
As we have seen, trace evidence is often undervalued despite its importance, and offers unique forensic potential in criminal investigations. It’s capacity to establish links between people, items, and places through microscopic material transfer provides essential data that may be unavailable through other forensic methods.
The hurdles encountered in trace evidence examination, such as the limited availability of specialized personnel, the financial burden of dedicated instruments, and the necessity for evidence-preserving techniques, demand forward-thinking solutions that optimize productivity and versatility.
The foster+freeman ffTA system directly responds to these issues with its adaptable architecture, providing a broad spectrum of analytical functions on a unified and economical platform. This strategy amplifies the effectiveness of skilled analysts by providing tools that maximise forensic value while ensuring a strong price-performance ratio.
To fully appreciate the potential of trace evidence and understand how the ffTA system can elevate your forensic work, we invite you to explore further, through our overview video below, on-demand trace evidence webinars, or the ffTA product page, which provides a detailed breakdown of each module and associated applications.
ffTA Overview Video
Watch our ffTA Product Showcase Video for more information on this powerful devices, and a demonstration of the modules discussed in this article.
On-Demand Trace Evidence Webinars
Webinar – Anti-Terror Forensics: Investigation and Identification in the event of a Terrorist Attack
Webinar – Forensic Hair and Fibre Detection Analysis