Fingerprints

Sex Determination Through the Chemical Analysis of Fingerprints
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Sex Determination Through the Chemical Analysis of Fingerprints

Fingerprints have been a staple of forensic science for decades, providing a reliable (though not perfect) means of identifying suspects and placing people at crime scenes. In recent years, scientists have turned their attention towards exploring the additional information that could be extracted from fingerprints, in particular, chemical information for police intelligence. Fingerprints are composed of a mixture of chemical compounds both excreted through our skin and picked up from the environment.

Over the past decade, analytical chemists have shown that there may be sufficient chemical differences in the fingerprints of male and female donors to differentiate between the sexes. By studying these chemical differences, it may be possible to build a model capable of predicting the sex of a fingerprint donor based on the chemical compounds within the fingerprint.

In a recent study published in Forensic Chemistry, a method was developed to predict the sex of a donor based on the presence of peptides and proteins in fingermarks. The study used MALDI-MS (Matrix-assisted laser desorption/ionization mass spectrometry), a type of mass spectrometry that enables both the measurement and identification of the chemical constituents in a material, in addition to the imaging of samples. MALDI has already been demonstrated to be a powerful technique in the chemical analysis of fingermarks, including imaging fingermarks and detecting the presence of blood and drugs in the mark. Much of the research in the area has been led by Professor Simona Francese of Sheffield Hallam University in the UK, senior author on this recent paper.

In the study, 199 participants donated multiple fingermarks, culminating in hundreds of samples for analysis. The fingermarks used for the analysis were natural, that is to say, deposited with no fingertip preparation beforehand. Many studies in the chemical analysis of fingerprints use “groomed” marks, in which the fingers are rubbed on the face or forehead in order to load the fingers with skin secretions prior to deposition. Although this provides rich samples for analysis, they are not applicable to fingermarks encountered in the real world.

After fingermark collection, MALDI-MS was then used to analyse the samples, focusing on the measurement of peptides and proteins in the deposited marks. To further mimic realistic scenarios, fingermarks were analysed both undeveloped and enhanced by common fingerprint visualisation techniques (white powder and vacuum metal deposition). Based on the chemical profiles produced, a predictive model was then constructed for the purpose of predicting the sex of the donor of unknown fingermarks, such as those that may be discovered at crime scenes.

The technique had a predictive power of up to 86%, demonstrating the potential to differentiate between male and female donors to a degree. There were, however, challenges in this study. Polyethylene glycol (PEG)-based contaminants, routinely used in cosmetics and personal care products, were commonly encountered, interfering with the detection of the actual targets of the analysis. Furthermore, the application of fingermark development techniques also caused interference, with many mass spectra being dominated by the gold nanoparticles used in the vacuum metal deposition method. This suggests the technique may only be truly applicable in the case of undeveloped fingermarks.

Although the technique has a high predictive power, it was not able to determine the sex of the donor in all cases, rendering it unsuitable for conclusively excluding suspects from an investigation based on their sex. However the method could be used to triage fingermarks, allowing investigators to establish which marks are of the greatest importance and which should be prioritised for further study, potentially speeding up forensic investigations.

 

Heaton & Bury et al. Investigating sex determination through MALDI MS analysis of peptides and proteins in natural fingermarks through comprehensive statistical modelling. 2020, Forensic Chemistry, DOI: 10.1016/j.forc.2020.100271

Fingerprint Technology to Prevent Pangolin Poaching
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Fingerprint Technology to Prevent Pangolin Poaching

Pangolins are amongst the most illegally trafficked mammals in the world, with hundreds of thousands being slaughtered each year for their meat and scales. In recent months, pangolins have gained extra attention due to their link to the spread of COVID-19, resulting in the Chinese government making efforts to control the use of pangolin scales in traditional medicine. All eight species of pangolin are protected and included on the International Union for Conservation of Nature’s Red List of threatened species, but this does not deter criminals from capturing and selling these animals.

In recent years forensic techniques have been harnessed in the fight against poaching and illegal animal trafficking, in particular with the aim of linking illegally traded animal materials to the perpetrator. Materials derived from animals pose a particular challenge for traditional fingerprinting techniques, with techniques often not being suitable for use on the likes of scales, feathers and skins of animals. Furthermore, in order for fingerprint development and collection techniques to be rolled out across relevant countries, the tools developed need to be easy to use, effective and inexpensive.

In a recent study published in Forensic Science International, a team of researchers at the University of Portsmouth developed a technique for lifting fingermarks from the scales of pangolins, demonstrating the potential to connect criminals to illegally traded pangolins via fingerprints. As an individual pulls scales from a pangolin, it is likely that fingermarks will be deposited on the scales. However, determining the best development technique for this unique material can be challenging.

The technique presented employs lifters which contain a soft gelatine material ideal for picking up traces and impressions when pressed against a surface. Low-adhesive gelatine lifters have been used in forensic practice for decades, particularly for lifting footwear marks and fingermarks off objects, but have not been widely applied in wildlife crime. The surface of a pangolin scale is uneven, containing voids that could be problematic for some development techniques. However, the soft nature of the gelatine allows the lifters to press into the voids and lift as much material as possible.

In this study, scales from varying African species of pangolin were provided by the UK Border Force for the assessment of the gelatine lifting technique. Of the marks lifted from pangolin scales, 74% exhibited ridge detail and 24% showed no ridge detail but evidence of contact. Once lifted, the fingermarks could then be imaged using a camera or mobile phone camera for rapid digitisation. Although only a pilot study, the research has demonstrated that the gelatine lifter could be easily applied to the scales of the pangolin and subsequently preserved for scanning and comparison, providing law enforcement with a potential route to identify poachers.

 

Moorat et al. The visualisation of fingermarks on Pangolin scales using gelatine lifters. Forensic Science International, 2020. DOI: 10.1016/j.forsciint.2020.110221

 

 

Developing Fingerprints on Metals to Aid Knife & Gun Crime Investigations
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Developing Fingerprints on Metals to Aid Knife & Gun Crime Investigations

Fingerprints are something of a staple in forensic science. For over 100 years we have used the unique details of fingerprints to identify victims and suspects, and draw connections between people and objects to place suspects at crime scenes. Fingermarks are encountered on all kinds of surfaces that can have an effect on how easy it is to visualise the mark and for how long the mark persists. As a result, the market is flooded with products for developing fingerprints, from powders to glues to chemical reagents.

Despite the options available, some surfaces, for instance metals, still prove somewhat tricky when it comes to developing prints. This is due to various factors, such as how the chemical results in the fingermark and developing reagents may react with the surface. This is obviously problematic when trying to obtain fingerprints from knives and firearms, a matter of particular importance right now worldwide. For years researchers have been examining methods of improving the detection of fingerprints on metals, including metal vapour deposition and different chemical reagents, but reliable techniques are still few and far between.

Researchers at the University of Nottingham and University of Derby in the UK are using analytical chemistry to solve this problem. Using a technique called Time-of-Flight Secondary Ion Mass Spectrometry, or ToF-SIMS, researchers have developed a way of producing images of fingerprints of various metal surfaces. ToF-SIMS utilises an ion beam which is passed along the surface of the sample, causing ions (charged chemical components) to be emitted from the sample. These are then analysed by mass spectrometry and the results used to produce a kind of map of the surface.

Researchers deposited fingermarks on various types of commonly-encountered metals, such as stainless steel and aluminium, and studied the effects of time on the ability to visualise the prints. Cyanoacrylate (or superglue) fuming, a traditional technique particularly popular when analysing metal surfaces, proved to be unreliable, with the print’s quality degrading rapidly or disappearing completely in just a matter of days. However using this new mass spectrometry-based approach, fingermarks could be visualised in samples up to 26 days old, a vast improvement on traditional methods.

The high-resolution images produced sufficient detail to not only observe ridge detail in the marks, but even the shape and position of individual sweat pores. Furthermore, and perhaps most importantly in a forensic context, the technique is non-destructive. Current methods of visualising fingerprints tend to involve adding a powder or chemical to the print, inevitably altering and potentially contaminating it. But the use of ToF-SIMS ensures the print remains intact, so further development or analysis techniques can be employed if required.

By enabling the visualisation of fingerprints that previous techniques may have failed to reveal, this method has the potential to not only aid investigators as they face the ongoing rise of knife and gun crime, but could also be applied to cold cases. However it is important to note that fingermarks deposited as part of research are not always indicative of real-world samples. In reality the fingerprints we leave behind can vary greatly in the amount of material deposited and the type of material being left behind. Traces of anything handled can be deposited in the fingermark, adding many potential variables to the real-world applicability of this kind of work. Despite this, the study demonstrates a promising new technique for the development of fingermarks on metals, which could have great implications in the investigation of violent gun and knife crimes.

 

Thandauthapani et al. Exposing latent fingermarks on problematic metal surfaces using time of flight secondary ion mass spectroscopy. Science & Justice. 2018, 58(6).

Drug Detection at Your Fingertips: Illicit Drugs in Fingerprint Sweat
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Drug Detection at Your Fingertips: Illicit Drugs in Fingerprint Sweat

Researchers have developed a new tool for the rapid detection of a number of illicit drugs using only the sweat of an individual’s fingerprint.

Typically, the procedure to test for drugs in human beings necessitates the collection of blood or urine and laboratory-based analysis by gas or liquid chromatography with mass spectrometry. Unfortunately these standard methods are somewhat invasive, require potentially time-consuming laboratory-based analysis, and use complex pieces of analytical instrumentation requiring a trained operator to use. They are inevitably unsuitable for rapid, in-situ screening of potential drug users.

Researchers at the University of East Anglia and Intelligent Fingerprinting Ltd (a spin-out company from the university) have been working on a method of conducting simple, rapid drug analysis using sweat from a person’s finger. The technique has been developed to detect four classes of drugs – cannabis, cocaine, amphetamines and opiates, with cannabis being detected based on the presence of Δ9-tetrahydrocannabinol (THC), cocaine on the presence of benzoylecgonine, and opiates via the detection of morphine.

The finger of an individual is firmly pressed onto the Drug Screening Cartridge. This is then filled with a buffer solution before insertion into the reader for analysis. Capable of detecting drugs down to the picogram level, the system is a fluorescence-based lateral flow competition assay containing four drug-bovine serum albumin conjugate lines on a nitrocellulose test strip.  In short, when a sample is introduced to the test strip, fluorescently-tagged antibodies pass over the conjugate lines. As these antibodies are specific to each drug class of interest, if that drug is present they will bind to the drug. At the end of the test, a fluorescence signal is measured. If none of the four drug classes were present, a maximum fluorescence signal will be obtained. However if any drugs were present to bind with the antibodies, there will be a decrease in the fluorescence signal proportional to the drug concentration. Within about 10 minutes, the device then gives a simple pass/fail response, requiring no specialist knowledge or excessive training to operate and interpret the results.

Furthermore, the technique has also been demonstrated to be effective when applied to the deceased. Researchers worked with a number of UK-based coroners to obtain fingerprint sweat samples from 75 deceased individuals. The most common drug detected was opiates, which is a logical finding considering the number of terminally ill patients who are prescribed morphine during palliative care.

In order to compare the new technique with those typically employed in the detection of drugs in human beings, analysis of blood samples was conducted by LC-MS-MS. The results between the two methods correlated well, with the accuracy between DSC of fingerprints and LC-MS-MS of blood being 88-97%, depending on the drug. This demonstrates the effectiveness of the method and its ability to stand up to existing techniques, though there are inevitably some shortcomings. Authors of the study have stated that there are known accuracy issues with lateral flow measurement devices, thus this new technology should be used as a presumptive screening method prior to confirmation by mass spectrometry. Furthermore, the range of target drugs is clearly currently limited, though future development could no doubt enable other classes of drug to be included.

Full details of the findings can be found in the Journal of Analytical Toxicology.

 

References

Hudson, T. Stuchinskaya, S. Ramma, J. Patel, C. Sievers, S. Goetz, S. Hines, E. Menzies and D. A. Russell, J. Anal. Toxicol., 2018, 6–10.

Forensic Magazine. Fingerprint Drug Screen Test Works on the Living and Deceased. [Available online] https://www.forensicmag.com/news/2018/10/fingerprint-drug-screen-test-works-living-and-deceased

 

Scientist Special: Galton, Herschel & Faulds – The Competing Pioneers of Fingerprinting
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Scientist Special: Galton, Herschel & Faulds – The Competing Pioneers of Fingerprinting

The use of fingerprints as a means of identification has been successfully implemented worldwide. But how did the idea of using these unique impressions in a forensic setting first come about? Many scientists are known to have been involved in the early research relating to fingerprinting, dating right back to the 1600s, but Sir Francis Galton and William Herschel are widely recognised as the real pioneers of forensic fingerprinting.

However the story actually begins with the work of another man: Henry Faulds. In the late 1880s, the Scottish physician was working in Japan in a number of roles, one of which caused him to be involved in various archaeological digs. During this time he first stumbled upon the uniqueness of fingerprints after discovering prints left behind by craftsmen in old pieces of ceramic pottery. This allegedly inspired his notion of using fingerprints to identify criminals, at which point he promptly published an article in Nature detailing his thoughts on the matter. In his manuscript, “On the Skin-Furrows of the Hand”, Faulds suggested the possibility of using fingerprints to identify individuals, however did not provide anything to support his theory other than the anecdotal evidence of his own use of fingerprints to identify the perpetrator of a break-in at his hospital. Back in the UK, Faulds shared his ideas with Scotland Yard, but they unsurprisingly had no interest in this somewhat unsupported theory. Incidentally, Faulds also shared his work with Charles Darwin. Although Darwin did not pursue the research himself, he did forward the information to his cousin, Francis Galton. At the time, nothing came of this interaction.

Shortly after Fauld’s publication in Nature, William Herschel, a British civil servant who was based in India at the time, soon published a responding letter in Nature claiming he had been using fingerprints as a means of identification for years. A very public argument over who should claim credit for this idea ensued between the two scientists which lasted for years, though the world paid little attention. There was quite simply no data to support the claims of the two men.

A couple of years later, Sir Francis Galton once again enters the picture. Now heavily involved in the field of anthropometry (the study of measurements of the human body), he began working with Herschel to gather the much-needed data necessary to support the theory of fingerprints as a means of identification. Galton’s research allowed him to collect thousands of fingerprints and ultimately conclude that fingerprints were in fact unique to the individual, could persist on a surface for years if not decades, and could be easily used to develop a system of storing and comparing prints. Galton presented his findings at the Royal Institution, sharing his and Herschel’s research in fingerprinting as a means of identification. Based on Galton’s work, the use of fingerprinting was finally considered by Parliament in 1894, and was soon implemented in criminal investigations. Galton and Herschel were now viewed as the original pioneers of forensic fingerprinting, whereas Faulds later spent years fighting to be recognised as the true founder, petitioning to academic journals, newspapers and even the Prime Minister.

In 1892, anthropologist Juan Vucetich made history by using fingerprint evidence to positively identify the culprit in a criminal case. When the children of Francisca Rojas were found murdered, Vucetich implicated Rojas when a bloody print allegedly proved she was the murderer. Since then, the study and use of fingerprints has been a fundamental aspect of forensic investigations worldwide.

References

Faulds, H. On the Skin-Furrows of the Hand. Nature, 1880, 22.

Stigler, S. M. Galton and Identification by Fingerprints. Genetics. 1995, 140(3), 857-860.

University of Glasgow. Henry Faulds. [online] Available: http://www.universitystory.gla.ac.uk/biography/?id=WH25214&type=P

Determining the Age of a Fingerprint: Is It Possible?
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Determining the Age of a Fingerprint: Is It Possible?

During the scrutinising examination of a crime scene, it is entirely plausible for dozens or more fingerprints and fragments of fingerprints to be recovered. Not at all surprising considering how often we touch endless surfaces in our day-to-day lives. Consider how many people might grasp the handle of a shop door in an average day. If that shop were to become a crime scene, how could one possibly distinguish between prints that had originated on the day of the crime and those deposited weeks or months ago? Is it possible to estimate the age of a fingerprint?

Firstly, a quick review of just what a fingerprint is. We all know fingerprints are a series of unique arches, loops and whorls left behind when we touch a surface. But people may be slightly less sure of what these deposits are actually composed of.

Although the composition of a fingerprint is somewhat complex, 95-99% of the deposit is simply water, which will typically readily evaporate. The remaining 1-5% is an intricate mixture of organic and inorganic compounds ranging from amino acids and fatty acids to trace metals. Chloride, potassium, sodium, calcium, hydrocarbons, sterols – the list goes on. A vast concoction of chemicals emitted through our skin and deposited whenever our fingertips touch a surface.

But what we didn’t know until recently, is that these deposited chemicals gradually move with time, and that this movement can be used to determine how long a fingerprint has been on a particular surface. Researchers from the National Institute of Standards and Technology recently stumbled upon this very fact (Muramoto & Sisco, 2015).

Fingerprint when freshly deposited (left) and after 72 hours (right). Credit: Muramoto/NIST

Fingerprint when freshly deposited (left) and after 72 hours (right).
Credit: Muramoto/NIST

Like many discoveries, the research itself was something of an accident. The NIST researchers were initially using analytical techniques to detect trace amounts of illicit substances present in fingerprints. In the process of this investigation, they noticed the movement of chemicals within the fingerprint over time. Fingerprints are made up of ridges and valleys forming unique patterns, the characteristic features that allow investigators to distinguish between prints deposited by different people. These features are imprinted in various chemicals when an individual leaves a print behind. However over time the chemicals composing the fingerprint begin to migrate, moving from the defined ridges of the fingerprint into the valleys, essentially blurring the details of the print.

The researchers focused on particular biomolecules, namely fatty acids such as palmitic acid. By depositing fingerprints on sterile silicon wafers and storing the samples under strictly controlled conditions for a period of time, scientists were able to clearly observe the migration of molecules using a technique known as time-of-flight secondary ion mass spectrometry (TOF-SIMS). After a period of only 1 hour after fingerprint deposition, the friction ridge patterns of the fingerprint were clearly visible with the fatty acid molecules under observation residing along the ridges of the print. However within 24 hours the molecules had diffused into the valleys, blurring the patterns of the fingerprint.

The research thus far has simply been conducted to prove the concept of fingerprint component migration for ageing fingerprints, but further work could investigate time effects on a greater scale and even differences in the migration of different molecules. Although the method is advantageous in that it does not depend on chemical changes in fingerprints, which can be very dependent on individual circumstances, further work would be warranted to establish how environmental differences could affect the rate at which this molecular movement occurs, including temperature and humidity effects as well as those caused by the deposition surface.

As intriguing as this research is, this is not the first time scientists have tried to devise a method of ageing fingerprints using chemistry. In fact, researchers have been attempting to accurately age fingerprints for decades. Research has focussed on the changes in the chemical composition of fingerprints over time. For instance, concentrating on a particular compound, such as cholesterol, and establishing the rate at which the concentration of that compound changes over time (Weyermann et al, 2011). Unfortunately many such studies have found changes in the chemical composition of fingerprints to be too variable and unpredictable, particularly when taking into account the differences between donors and the effects of different conditions. Other studies have attempted to determine the age of a fingerprint based on how well powder adheres to the ridges (Wertheim, 2003), by changes in fluorescence wavelength over time (Duff & Menzel, 1978), and changes in electrostatic charge with time (Watson et al, 2010). A vast array of scenarios have been studied intently.

A method of establishing the age of a deposited fingerprint has been at the forefront of latent print research for a long time, and is likely to continue. Although fascinating advances have been made, scientists are a long way from catching criminals by the age of a fingerprint.

References

Cadd, S. Islam, M. Manson, P. Bleay, S. Fingerprint composition and aging: A literature review. Sci Justice. 2015(55) pp. 219-238.

Duff, J. Menzel, E. Laser assisted thin-layer chromatography and luminescence of fingerprints: an approach to fingerprint age determination. J. Forensic Sci. 1978(23), pp 129-134.

Muramoto, S. Sisco, E. Strategies for Potential Age Dating of Fingerprints through the Diffusion of Sebum Molecules on a Nonporous Surface Analysed Using Time-of-Flight Secondary Ion Mass Spectrometry. Anal Chem. 2015(87) pp. 8035-8038.

National Institute of Standards & Technology. Who, What, When: Determining the Age of Fingerprints. [online] Available: http://www.nist.gov/mml/mmsd/20150824fingerprints.cfm

Watson, P. Prance, R. J. Prance, H. Bearsmore-Rust, S. T. Imaging the time sequence of latent electrostatic fingerprints. Proc. SPIE ‘Optics and photonics for counterterrorism and crime fighting VI, Toulouse, 7838, 783803-1-6, ISBN 9780819483560 (2010).

Wertheim, K. Fingerprint age determination: is there any hope? J. Forensic Identif. 2003(53), pp 42-49.

Weyermann, C. Roux, C. Champod, C. Initial Results on the Composition of Fingerprints and its Evolution as a Function of Time by GC/MS Analysis. J. Forensic Sci. 2011(56), pp 102-108.

Forensic Failures: The Shirley McKie Fingerprint Scandal
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Forensic Failures: The Shirley McKie Fingerprint Scandal

In light of the recent FBI hair analysis outrage, it seemed appropriate to revisit an old classic in the history of failing forensic science. The Shirley McKie fingerprint scandal. Back in the 1990s, Shirley McKie was a police constable whose life, along with an important murder investigation, was essentially ruined due to mistakes made by forensic experts.

At the beginning of 1997, 51-year-old Marion Ross of Kilmarnock, Scotland was found murdered in her home, with suspicion quickly falling on David Asbury, a handyman who had previously carried out some work on the house. A number of fingerprints were recovered throughout the investigation, including one belonging to Asbury on a gift tag in the victim’s home. Further incriminating Asbury was a tin containing nearly £2,000 found in his house, which incidentally had the victim’s fingerprints on.

But by far the most controversial piece of evidence in this case was another fingerprint recovered from the crime scene which did not belong to neither the victim nor the suspect. A thumbprint was recovered from a doorframe at the murder scene and, according to the experts of the Scottish Criminal Record Office (SCRO), that thumbprint belonged to police constable Shirley McKie.

One might think the fingerprint of a police officer at a crime scene is nothing of great note, though perhaps some slightly sloppy police work, however that was not the case. Because in this instance, Shirley McKie adamantly denied that she had ever set foot in the victim’s house. So how did her fingerprint materialise at this crime scene? Well, it didn’t. McKie was telling the truth.

Unfortunately for McKie, her claims fell on deaf ears and she was subsequently suspended, fired and then arrested by Strathclyde Police in 1998 and charged with perjury (lying under oath), even though not one of the dozens of police staff involved could recall seeing her at the crime scene. A gruelling trial ensued, dragging both McKie’s reputation and life through the mud, along with the reliability of fingerprint evidence. Four fingerprint experts from SCRO concurred that the fingerprint belonged to McKie, the same experts who had identified the fingerprint found in Asbury’s home as belonging to the victim.

The fingerprint evidence in this case became something of a double-edged sword. If the latent print comparison conducted by the SCRO was accurate, Asbury could be reasonably named as the perpetrator but Shirley McKie would surely be lying about visiting the crime scene. Conversely, if McKie was truthful in her statement, then the fingerprint evidence was flawed and the evidence against the suspect useless. With the fingerprint identification being the only significant evidence incriminating Asbury, it naturally became a vital aspect of the case. At this point in time fingerprint evidence was perhaps viewed as an infallible gold standard in forensic science, and the jury agreed that the latent print evidence presented by the SCRO was accurate, thus Asbury was convicted and McKie assumed just as guilty.

Fingerprint comparison can be a subjective technique (www.clpex.com)

Fingerprint comparison can be a subjective technique (www.clpex.com)

Thankfully the investigation did not end there. Two fingerprint experts from the U.S. were called upon to offer their expertise, and both declared that the mysterious fingerprint found in the victim’s home did not belong to McKie. The SCRO experts had misidentified the fingerprints, although they stubbornly refused to admit to this. Furthermore, a member of the Scottish Parliament somewhat unusually invited fingerprint experts from around the world to examine the prints. 171 experts from numerous countries all reached the same conclusion – that the two latent prints did not match.

The fingerprint evidence was ultimately rejected and McKie was unanimously cleared of all charges. Perhaps too little too late for a woman who had lost her reputation and career. With the fingerprint evidence rejected and McKie’s name cleared, Asbury’s conviction was also overturned, with there being nothing more than mere circumstantial evidence linking him to the crime. So through this misinterpretation of fingerprint evidence, not only was Shirley McKie’s career ruined and the freedom of a potentially innocent man put on the line, but a murder investigation was left unsolved with little likelihood of ever finding the real killer of Marion Ross.

Over the years following this trial, a number of inquiries were conducted examining why this incident was allowed to occur in the first place. Through the public inquiry it was ultimately concluded that McKie had simply been the victim of human error and nothing more, though many argued at the time that there had been something of a conspiracy and cover-up. The inquiry called for competency training of analysts and for independent reviews to be carried out of any fingerprint evidence that is disputed, along with a prompt change in the way in which fingerprint comparisons were made in the first place.

Most importantly, it was recommended that fingerprint evidence should be viewed as opinion evidence only as oppose to the product of a scientific technique that can produce absolute answers, and that experts should not make claims with 100% certainty. This problem has been once again highlighted in the recent FBI scandal, in which hair analysis experts overstated the evidence, implying the analysis was far more reliable than it actually was. Members of the jury are unlikely to have any significant knowledge of forensic techniques utilised by experts, thus are hardly in a position to determine the reliability of the methods used. It is up to the expert to highlight just how dependable the evidence really is.

Although the Shirley McKie case offered a slight silver lining in highlighting the fallibility of forensic evidence, this is evidently a lesson that is yet to be taken onboard.

References

The Guardian. Fingerprint evidence ‘based on opinion rather than fact’. [online] Available: http://www.theguardian.com/uk/2011/dec/14/fingerprint-evidence-opinion-fact

McKie, I. A. J. ‘There’s name ever fear’d that the truth should be heard but they whom the truth would indite’ (Presentation given by Iain McKie to the Forensic Science Conference 2003. Sci Justice. 43 (2003), pp. 161-165.

University of Dundee. ‘Road map for reform’ of fingerprint practices to be developed at the Scottish Universities Insight Institute. [online] Available: http://app.dundee.ac.uk/pressreleases/2011/december11/fingerprint.htm

Caught Red-Handed: MALDI Mass Spectrometry & Bloodied Fingerprints
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Caught Red-Handed: MALDI Mass Spectrometry & Bloodied Fingerprints

Most previous methods of establishing whether a fingermark at a crime scene contain blood are purely presumptive. The suspected fingermark, whether it be a print merely contaminated with traces of blood or an entire mark left in blood, will be subjected to tests which will aim to confirm or refute the presence of blood. However most existing presumptive tests suggest that it is a possibility the fingermark in question contains blood… but that it equally could be another similar substance that happens to produce a positive response with the test used. Thus is the limitation of any presumptive test – they can only give a possibility, not a definitive answer. Obviously not ideal during a forensic investigation.

Suspected bloodstains can be subjected to a wide range of tests to ascertain their composition. Blood may be visualised using alternative light sources, but this is a far cry from confirming its composition and in some cases (such as with the use of short-wave ultraviolet light) can even be destructive to DNA, thus obviously not ideal for the forensic examination of a blood sample. Spectroscopic techniques such as Raman spectroscopy have proved successful in potentially distinguishing blood from other biological fluids, though this has not been widely applied, particularly to blood in fingermarks. Chemical enhancement techniques have also been developed in the past, such as those that react with amino acids or haem-reactive compounds present to produce a colouring or fluorescence to enhance the blood. As successful as these methods may have been in the past, they are still only presumptive and cannot claim with any kind of near-certainty that any positive reaction produced is the result of blood and furthermore whether that blood is of human origin.

As a result of this, more confirmatory tests are needed.

More affirmative procedures do exist and are currently being developed. A particularly interesting method of detecting blood in fingermarks is using a technique known as MALDI MS. That is, Matrix-Assisted Laser Desorption Ionisation Mass Spectrometry. This relatively new analytical technique (relative to the history of mass spectrometry anyway) is most commonly applied to determining the mass of peptides, proteins and polymers, so is ideal for focusing on certain components of blood.

For those unfamiliar with mass spectrometry, in its simplest form it is a technique which is used to determine the identity of sample components based on their mass-to-charge ratio and, in some cases, how the molecule fragments when ionized. MALDI is something of a variation of this technique. In this technique, the sample to be analysed is mixed with a particular matrix material and applied to a plate. A laser irradiates the sample and matrix, causing ablation and desorption, after which the sample is ionized and then accelerated and detected using mass spectrometry.

Researchers have applied MALDI MS to detecting the presence of blood by specifically focusing on the detection of haem and haemoglobin molecules based on their mass-to-charge ratios. These molecules are vital components of blood, with haemoglobin being the protein responsible for oxygen transportation and haem being a compound embedded into haemoglobin which provides the iron essential for oxygen binding. By subjecting known and suspected blood stains and bloodied fingermarks to this technique, haemoglobin chains could be detected even in traces of blood invisible to the naked eye. Initial research into this technique studied human, equine and bovine haemoglobin, establishing that it is possible to determine whether or not haemoglobin was from a human source using mass spectrometry at a high mass range. Both fresh and aged blood samples could be successfully analysed, making the application potentially beneficial to samples from various points in time. Furthermore, the technique has proven to be compatible with other methods often used by investigators when attempting to enhance fingermarks at incident scenes, meaning the new method is not likely to interfere with existing procedures.

A typical haemoglobin molecule.

A typical haemoglobin molecule.

This fascinating application of matrix-assisted laser desorption ionisation mass spectrometry offers a whole new world of possibilities in blood detection in forensic science. Although at present such instrumentation is far from being the norm in the forensic scientist’s arsenal, the applications of advanced mass spectrometry techniques to answering some of the simpler yet vital questions during a criminal investigation make for a captivating read.

References

Bradshaw, R et al. Direct detection of bloos in fingermarks by MALDI MS profiling and imaging. Science and Justice. 45 (2014), pp. 110-117.

King’s College London. An Introduction to Mass Spectrometry Based Proteomic. [online][Accessed 16 Feb 2015] Available: http://www.kcl.ac.uk/innovation/research/corefacilities/smallrf/mspec/cemsw/instr/Mass-Spec-based-Proteomics.pdf