Month: November 2014

Saliva for Cracking Down on Drink-Drivers
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Saliva for Cracking Down on Drink-Drivers

The intake of alcohol for leisure is common all around the world, and many of us indulge every now and then (some more so). But we’re all also aware of the effects of alcohol and how it can play a big part in criminal activities, ranging from drunken street brawls to homicide. In fact according to the National Council on Alcoholism and Drug Dependence, in the case of 40% of convicted murderers in the US alcohol was a factor in the crime. But of course most commonly in legal investigations, focus on alcohol consumption is most commonly related to driving.

In the United Kingdom, people suspected of drink-driving are typically pulled over and breathalysed at the roadside. If they fail the test (i.e. they are over the legal limit of 80mg per 100ml of blood), they will be taken to a police station and breathalysed once again. Typical breathalysers work by measuring the concentration of alcohol in a person’s breath (note I say in their breath, not strictly their bloodstream – two very different things). After consumption, a certain amount of alcohol will leave the body via the breath, thus allowing us to pretty accurately calculate a person’s blood alcohol content.

booze

But a primary disadvantage of the breathalyser test is that it cannot be repeated. Once the alcohol is out of the individual’s system, the proof of their blood alcohol content is gone. And as with many types of scientific analysis, a certain margin of error will exist. Furthermore, what if a breathalyser test is simply not plausible? Either because the suspected drink-driver is not able to provide a breath sample or they are making all attempts possible to avoid it (a certain Brighton-based woman who continued to have an alleged panic attack to avoid giving a sample, for instance). In short, there are numerous flaws in the use of breathalysers, and there’s no chance of an accurate retest further down the line if for whatever reason the original sampling comes under scrutiny.

But what if a biological sample could be collected at the time, stored and subjected to future analysis as needed, and even repeat measurements taken if required? A blood sample is surely perfect for this. But on the other hand, this is a fairly invasive procedure that will not necessarily be appropriate in all situations. How about a simple saliva swab?

A number of healthy subjects ingested enough beer to achieve 0.5g ethanol per kg of body weight, after which saliva, urine and breath samples were collected at 10, 30, 60 and 90 minute intervals following alcohol intake. The breath samples were taken using a standard breathalyser, and bodily fluids were subjected to analysis by gas chromatography with a flame ionisation detector (GC-FID). The results correlated well, indicating that the analysis of saliva could well be a suitable alternative for monitoring the alcohol levels in individuals.

The use of saliva to test alcohol levels is not strictly novel, as there are alcohol test strips available for use with saliva. However as with most tests such as these, they are simply presumptive, meaning some additional form of analysis is required for confirmation. But a procedure involving the immediate collection of a sample that can be stored for future analysis along with a confirmatory analytical technique such as gas chromatography can instil more confidence in both drink-driving scenarios and numerous other medico-legal situations.

References

Bueno, L. H. P. et al. Oral fluid as an alternative matrix to determine ethanol for forensic purposes. Forensic Sci. Int. 2014 (242), pp. 117-222.

National Council on Alcoholism and Drug Dependence. Alcohol and Crime. [Online][Accessed 30 November 2014] Available from: https://ncadd.org/learn-about-alcohol/alcohol-and-crime

Ammo Analysis: Using Isotopes to Match Bullets
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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

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Scientist Special: Edmond Locard

“Any action of an individual, and obviously the violent action constituting a crime, cannot occur without leaving a trace” – Edmond Locard

It seems apt to kick off Locard’s Lab with a brief post about the man behind the name – Edmond Locard. Every forensic scientist and his dog have heard the statement “every contact leaves a trace”, and Locard is the scientist responsible for coining the phrase.

locard

Born in 1877, a young Edmond Locard began his career by studying medicine in Lyon, France. He soon developed a particular interest in the application of science to law, producing a thesis entitled “Legal Medicine under the Great King”. Not only did he excel in the field of medicine, but he also later went on to study law and successfully passed the bar exam. Locard worked under medico-legal expert Alexandre Lacassagne, the gentleman famous for essentially fathering the field of criminology. His links with famous forensic experts did not end here, as he later studied alongside anthropologist Alphonse Bertillon, known for his work with anthropometrics. In 1910 Locard moved on to found the world’s first police laboratory in the attic of a courthouse, in which legal evidence could be collected and analysed. It took two years for Lyon police to actually recognise the laboratory.

Locard’s famous phase, “every contact leaves a trace”, became known as Locard’s exchange principle. The theory states that when two objects come into contact, each will leave some trace on the other. This exchange theoretically means that there will always be some evidence of the perpetrator at a crime scene to provide investigators with a link (of course this is simpler in theory than in practice). Perhaps his most famed publication was Traité de Criminalistique, or Treaty of Criminalistics, a vast seven-piece volume that detailed forensic techniques and ideas that are still used today.

In true dedication to his work, Locard continued his research right up until his death in 1966.

 

References

Chisum, W.J. Turvey, B. E (2011). Crime Reconstruction. California: Elsevier Inc.

Erzinclioglu, Z (2004). The Illustrated Guide to Forensics – True Crime Scene Investigations. London: Carlton Pub. Co.

Stauffer, E. 2005. Dr Edmond Locard and Trace Evidence Analysis in Criminalistics in the Early 1900s: How Forensic Sciences Revolve Around Trace Evidence. [Online] [Accessed 18 November 2014] Available from: http://www.swissforensic.org/presentations/assets/aafslocard.pdf