Determining the Age of a Fingerprint: Is It Possible?

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.

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Forensic Case Files: Bruce Ivins and the Anthrax Attacks

Forensic Case Files: Bruce Ivins and the Anthrax Attacks

In September 2001, when the US was still reeling from the notorious 9/11 terrorist attacks, two US Senators and various media organisations were sent letters containing spores from the bacterium Bacillus anthracis, the cause of the disease Anthrax. The malicious mail resulted in the deaths of five people, the infection of 17 others and an investigation between the FBI and the US Postal Inspection Service that spanned almost 7 years.

Bacillus anthracis is a rod-like bacterium which can, upon entering the body, bring about the acute disease known as Anthrax. The endospores (spores) of the bacterium can lay dormant for years, but become activated and multiply after coming into contact with a host. Once contracted, the symptoms of the disease are dependent on the route by which the bacteria entered the body. However left untreated, the disease can ultimately kill the host.

The mailed anthrax spores were accompanied by misleading letters suggesting the attack was motivated by religion, though the prospect of terrorist groups, that were already at the forefront of the country’s mind, were soon discounted. It was soon concluded that a likely source of the anthrax, which was of the Ames strain, had been maintained by the US Army Medical Research Institute of Infectious Diseases (USAMRIID). Suspicion fell on Dr Bruce Ivins, who had been a researcher at the facility. Whilst in this position, Ivins had created and maintained this particular spore-batch, suspected to have been the batch used in the anthrax attack. With suspicions supported by an array of incriminating circumstantial evidence, investigators called upon a team of scientific experts to establish whether there was a link between Ivins’ own anthrax and the mailed anthrax.

anth2

Traditional forensic techniques were used in the examination of the spore powder and the letters and envelopes, including fingerprinting, and hair and fibre analysis, though this did not lead to any major breakthrough. A suite of analytical techniques was employed to ascertain various facts regarding the anthrax. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to identify the size, shape and quality of the anthrax spores, as well as provide a profile of the chemical elements within the spores. SEM and TEM are microscopy techniques which employ a focused beam of electrons which interacts with the atoms of the sample, allowing it to be visualised. They can be coupled with energy-dispersive X-ray (EDX) spectroscopy to provide elemental analysis. The physical and chemical characteristics of the spores allowed investigators to presume that the anthrax was not weapons-grade, but it was of a concentration and quality similar to that used in bio-defence research.

Inductively coupled plasma optical emission spectroscopy (ICP-OES), a technique based on the emission of photons from substances, was used to provide further details of the elemental composition of the spore powder. Furthermore, gas chromatography mass spectrometry (GC-MS) was employed to characterise the spores. Experts at the Center for Accelerator Mass Spectrometry (CAMS) were called upon to analyse the anthrax spores and establish their relative age. Accelerator mass spectrometry turns a sample, which has been converted into solid graphite by the analyst beforehand, into ions and accelerates these ions to high kinetic energies before conducting mass analysis to detect C14 (and potentially other isotopes depending on the work) to estimate the age of a sample. The analyses carried out on the samples in this instance determined that the mailed anthrax has been produced within 12 months of the attack, narrowing down the possible sources and suspects.

But perhaps the biggest breakthrough in the case came from a newly developed DNA fingerprinting technique which allowed investigators to conclude that the blend of anthrax spores created by Ivins in the lab was identical to that used in the attack, though how unique this “genetic signature” was has been somewhat debated. The US Justice Department later concluded that Ivins was solely responsible for the preparation and mailing of the deadly spores, claiming that he believed the scare would resurrect his anthrax vaccine program. Ivins later died from an overdose, deemed to be a suicide.

The case of Dr Ivins and the anthrax letters is a great example of how different analytical techniques can be drawn together to work in perfect harmony, utilising their individual powers to find out everything there is to know about a sample. In this case the array of techniques used allowed investigators to discover what the spores looked like and what they were composed of, their concentration and quality, and even how old they were. Armed with this information, investigators could home in on the source of the anthrax spores and the man behind the attack.

References

Centre for Infectious Disease Research and Policy. FBI says it easily replicated anthrax used in attacks.

US Department of Justice (2010). Amerithrax Investigative Summary. Darby, PA: DIANE Publishing.

Washington Post. FBI investigation of 2001 anthrax attacks concluded; U.S. releases details. [online] Available: http://www.washingtonpost.com/wp-dyn/content/article/2010/02/19/AR2010021902369.html

Caught Red-Handed: MALDI Mass Spectrometry & Bloodied Fingerprints

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

Ammo Analysis: Using Isotopes to Match Bullets

Ammo Analysis: Using Isotopes to Match Bullets

We’ve all seen the classical TV crime drama clip where the over-worked genius detective throws a couple of bullets under the comparison microscope, lines up a set of striations and declares that the two bullets were fired from the same gun or maybe they came from the same box of bullets. Whilst this may be the crux that solves the case in fiction, and very occasionally in reality, linking bullets is typically not so simple. A more accurate method of connecting objects such as projectiles is to study them at an elemental level or, in the case of this research, at an isotopic level.

bullet-408636_1280

Elements exist as a number of different stable isotopes (atoms of the same element differing in the number of neutrons present in the nucleus). Lead, a common component in bullets, exists as four isotopes in nature; 204Pb, 206Pb, 207Pb and 208Pb. When lead occurs naturally in ore (a type of rock containing minerals and metals), different sources of lead will vary in their isotopic compositions. Further dissimilarity arises through recycling of lead products, meaning that lead from numerous sources may be mixed together into a new product. This variation can be utilised to distinguish between lead bullets from different batches or conversely establish that two bullets are likely to have originated from the same source.

The research we’re talking about here, led by a team at the University of Oslo in Norway, used an analytical technique called MC-ICP-MS to analyse the lead isotopic compositions of a range of bullets, cartridge cases and firearm discharge resides.

What’s MC-ICP-MS, I hear you ask?

MC-ICP-MS stands for multiple-collector inductively coupled plasma mass spectrometry. Put simply, a conventional ICP-MS involves the introduction of the sample as a fine aerosol, using an inductively coupled plasma source to ionise the sample, after which the newly ionised components are separated based on their different mass-to-charge ratios. The ions impact with a dynode of an electron multiplier, resulting in the release of an electron for each ion strike. This can then be amplified until an intensity significant enough for measurement is achieved. The signal is ultimately proportional to the ion concentration, therefore allowing for the amount of a substance present to be determined. Multiple detectors (such as MC-ICP-MS) use multiple detectors to simultaneously measure separated isotopes.

Figure 1: ICP-MS Schematic (http://www.spectro.com)

ICP-MS Schematic (http://www.spectro.com)

Okay, that concludes our technical talk! But now just what did this research find, and why is it useful?

After extracting lead from a wide range of bullet samples using nitric acid and subjecting the specimens to MC-ICP-MS, researchers could examine the distribution of isotopic ratios in bullets across a variety of manufacturers. Not only did it seem possible to distinguish between bullets from different manufacturers based on lead isotopic composition, but also between boxes of bullets from the same manufacturer produced at different times. In many instances fired bullets will become disfigured upon impact, making microscopic examination difficult if not impossible. But by studying the bullet at an isotopic level and even determining a kind of isotopic fingerprint, analysts may be able to distinguish between bullets produced in different regions of the world, by different manufacturers, and even between individual batches from the same company. The ability to do this could prove invaluable to forensic investigators.

Though naturally there was a certain amount of uncertainty associated with the work, the use of isotope ratios in the study of bullets proves promising. The idea of utilising isotopic ratios to distinguish between bullets is not a new concept, with researchers investigating the theory as early as 1975.  But as analytical techniques progress and improve, forensic scientists are able to obtain much more from their evidence, bettering the criminal justice system one isotope at a time.

References

Sjastad, K-E. et al. Lead isotope ratios for bullets, a descriptive approach for investigative purposes and a new method for sampling of bullet lead. Forensic Sci. Int, 244 (2014), pp. 7-15.

Perkin Elmer. The 30-Minute Guide to ICP-MS. [Online][Accessed 20 November 2014] Available from: http://www.perkinelmer.co.uk/PDFs/Downloads/tch_icpmsthirtyminuteguide.pdf