Forensic Acarology

Forensic Acarology is super exciting. What is forensic acarology I hear you cry?

WELL my little chums, I shall tell you. It is a little known and never practised, purely hypothetical branch of forensic entomology- it is -drum roll please- use of mites in criminal investigations! It’s basically to used as other trace evidence.

Trace Evidence

Trace evidence is a term used to describe materials found at a crime scene, or on a suspect/victim which because of their size, or texture are readily transferable from one location, or person, to another and persist there for some period of time [1].   The importance of trace evidence in criminal investigations was first shown by the 20^th century forensic scientist Edmund Locard, who stated “with contact between two items, there will be an exchange”, essentially meaning if the perpetrator came into contact with the scene of a crime, he would bring something into the scene that wasn’t there before, and take something away. Locard observed that be examining the nature and extent of this exchange, suspects/victims can be associated with evidence or locations [2]. As Trace evidence has proved invaluable in many criminal investigations, as discussed below, to connect suspects to crime scenes and other evidence, collecting the trace evidence and properly labelling and analysing it is a field of great importance. As trace evidence is by definition transitory and small, it’s presence will not often be visible to the naked eye, so recovery relies heavily on understanding how these traces transfer and persist, and how best to collect what may remain after contact [1]. The handling of trace evidence can greatly affect the outcome of criminal investigations, as the following two cases, from before the era of touch/trace DNA focus will show. In 1977, the 77 year old Rosa Simper of Adelaide was found in her bed strangled, with blunt force trauma to the head, and with signs of sexual assault with a foreign object. Vast amounts of trace evidence were collected from the bed, however it was from here that the investigation suffered. Paint and metal particles at an assumed [not counted] ratio of 75:25 were found, and implicated a spray painter by the name of Charles Edward Splatt as his clothing had a similar paint:metal ratio. This evidence lead to the investigation focusing on simply proving Splatt guilty, rather than truly assessing the evidence. From there onwards the trace evidence, such as a seed endosperm, was analysed with a view to implicate Splatt. The seed was compared to the seed used by Splatt in his aviary, and when found to match no further questions such as “How common is this seed?” “how common are aviaries?” were asked. The splitting of the trace elements, that is to say not considering the whole view of the case, meant it was impossible to consider other hypotheses with the benefit of a broader context. Splatt was eventually released due to mishandling of the forensic evidence [1]. The case of Frances Tizzone, conversely shows how proper use of trace evidence had secure a conviction. Tizzone’s body was found in a ditch by the side of a busy road in Australia, fully clothed and wearing boots with prominent soles, and attached to the soles were fibres. The investigator made detailed notes, and took images of exactly how the fibres were attached, before packaging the shoes up to ensure the fibres weren’t lost. This meticulous recording and collection of the trace evidence would prove to be vital to the case. After careful evaluation some of the fibres were found to be from a carpet, only used in a specific model of car, only 200 of which were imported to Australia, one belonging to an ex-boyfriend Tizzone had a stormy relationship with. After extensive experimentation to see how long such fibres would persist on the soles of boots, it was proved that the fibres would not persist for any extensive length of time, showing Tizzone’s contact with her ex-boyfriends car occurred directly before she was dumped in the ditch [1]. This case shows how the proper recognition, recording and analysis of trace evidence can make or break a case.

Trace evidence can be anything that transfers from one material or person to another, including, but not limited to, fingerprints, saliva and semen, fibres, glass, soil, hair, paint chips, gunshot/explosive residue and microscopic arthropods.

So far the trace evidence discussed as all been abiotic, however there are biotic factors to consider as well. Entomology has long been used in criminal investigations, as the presence of certain insects is an excellent way of telling not only where a corpse has been, but for how long at has been in those environments, and how long the body has been dead. However there are arthropods that have more scope than simply indicators of post-mortem intervals or location; Mites. Mites are ubiquitous, habitat-specific and highly diverse, and because of this are of great value in the analysis of trace evidence.  As mites are microscopic, they can be picked up or transferred without the host having any idea, and as they have DNA, they have the potential to provide more evidence- as even if the species of mite in question is abundant in many locations, it’s DNA might provide evidence that it is from a particular colony. Mites as trace evidence can be used in different ways; to link a suspect to a crime scene or body or to link a victim or cadaver to a location. Mites only found in outdoor environments can be used as trace evidence to give evidence about the transportation of a body for instance. Phytophagous mite juveniles can survive on decaying leaves associated with a corpse, whereas Canopalpus pulcher mites are only found associated with unsprayed apple trees, presence of those mites would indicate the body at some point being in such an environment. Mites that live in aquatic environments have a similar use, that is to say if mites which are specific to swimming pools for instance are found on a corpse, the implication is the body has been in such an environment[9]. Demodex mites, those which cause scabies, are lifted off the skin surface using Standard skin Surface Biopsy [SSSB] technique- a clean microscope slide with a drop of cyanocrylate glue on the centre is pressed against the skin in 3 areas- the nose, forehead, and cheeky, left for 60seconds then removed [10]. Mites present on/in the skin will attach to the glue, and can be further studied and identified under a microscope.

Due to the ubiquity and specificity of mites, they could prove very useful in criminal investigations- connecting a suspect to a crime scene. Analysis of the mites on the clothing of a suspect or victim could yield some important evidence. Collection of mites from clothing is done by lifting- using clear adhesive tape to press against the material, which is then stuck to a transparent sheet of plastic and viewed under a microscope. There has not been a great deal of research into the best techniques to maximise the amount of mites lifted from materials.

YET.

As you might have noticed, the tone of this post changed after the first two lines, as the bulk of this writing I did last year when I began my forensics obsession.  I will keep you updated as to where the field of Forensic Acarology goes next…There is research being done, and trust me I have an eagle eye on it!

References

1 Robertson, J.  and Roux, C., 2009. Trace Evidence:  Here today,  gone tomorrow? Science and Justice 50 (1) 18-22

2 Chisum, WJ. and Turvey, B. 2000. Evidence Dynamics: Locard’s Exchange Principle & Crime Reconstruction, Journal of Behavioral Profiling 1

3 Martin, AJP. 1940. Tribo-electricity in wool and hair.  Proceedings of the Physical  Society 53 186–189.

4  Deedrick, D. 2000. Hair, Fibres, Crime and Evidence.  Part 1: Hair Evidence. Forensic science communications  2(3)

5 Wiltshire, PEJ. 2006. Hair as a source of forensic evidence in murder investigations. Forensic Science International 163(3)  241-248

6. Roux, C. et al. 1995. Fibre transfer experiments onto car seats. Science and Justice 36 143-151

7 Ruffell, A and Sandiford, A. 2011. Maximising trace soil evidenced: An improved recovery merthod developed during investigation of a $26million bank robbery. Forensic Science International 209(1-3) e1-e7

8 Trejos, T and Almirall, JR. 2005. Sampling strategies for the analysis of glass fragments by LA-ICP-MS: Part 1. Micro-homogeneity study of glass and it’s application to the interpretation of forensic evidence. Talanta 67[2] 388-395

9 Perotti MA et al 2009. Forensic Acarology: an introduction. Experimental and applied acarology 49

10 Özdemir MH et al 2003. Investigating demodex in forensic autopsy cases. Forensic science international 3 226-231