Light in Forensic Science: Issues and Applications: Volume 17 (Comprehensive Series in Photochemical & Photobiological Sciences) - Hardcover

Hardcover

ISBN 10: 1782627685 ISBN 13: 9781782627685

Publisher: Royal Society of Chemistry, 2018

Synopsis

This book details the analysis of forensic evidence by light-based techniques, as well as the negative effects of light in the degradation of samples.

About this title

From the Back Cover

The identification and quantification of material present and collected at a crime scene are critical requirements in investigative analyses. Forensic analysts use a variety of tools and techniques to achieve this, many of which use light. Light is not always the forensic analyst's friend however, as light can degrade samples and alter results.

This book details the analysis of a range of molecular systems by light-based techniques relevant to forensic science, as well as the negative effects of light in the degradation of forensic evidence, such as the breakage of DNA linkages during DNA profiling. The introductory chapters explain how chemiluminescence and fluorescence can be used to visualise samples and the advantages and limitations of available technologies. They also discuss the limitations of our knowledge about how light could alter the physical nature of materials, for example by breaking DNA linkages during DNA profiling or by modifying molecular structures of polymers and illicit drugs. The book then explains how to detect, analyse and interpret evidence from materials such as illicit drugs, agents of bioterrorism, and textiles, using light-based techniques from microscopy to surface enhanced Raman spectroscopy.

Edited by active photobiological and forensic scientists, this book will be of interest to students and researchers in the fields of photochemistry, photobiology, toxicology and forensic science.

Excerpt. © Reprinted by permission. All rights reserved.

Light in Forensic Science

Issues and Applications

By Giorgia Miolo, Jacqueline L. Stair, Mire Zloh

The Royal Society of Chemistry

Copyright © 2018 European Society for Photobiology
All rights reserved.

ISBN: 978-1-78262-768-5

Contents

Chapter 1 Light for Crime Scene Examination Valerio Causin and Giuseppe Guzzini, 1, 
Chapter 2 Degradation and Damage due to Exposure to Light in Trace Evidence Valerio Causin, 27, 
Chapter 3 Use of Light in the Detection of Genetic Variation of Forensic Importance Nick Dawnay, 51, 
Chapter 4 Use of Light in Fingerprint Detection Laurent Galmiche, Clémence Allain and Gilles Clavier, 83, 
Chapter 5 Light as an Ionizing Agent in Mass Spectrometry. Microbial Identification by Matrix Assisted Laser Desorption Ionization–Mass Spectrometry Donata Favretto and Pietro Traldi, 111, 
Chapter 6 The Use of Light in Forensic Glass Analysis Claire Gwinnett and Roger Robson, 143, 
Chapter 7 A Review on Analytical Techniques Used for Forensic Fiber Analysis Nirvani Mujumdar and Andres D. Campiglia, 175, 
Chapter 8 Novel Psychoactive Substances (NPS) and Recent Scenarios: Epidemiological, Anthropological and Clinical Pharmacological Issues J. M. Corkery, L. Orsolini, D. Papanti and F. Schifano, 207, 
Chapter 9 Raman Spectroscopy for the Analysis of Novel Psychoactive Substances (NPS) Jesus Calvo-Castro, Amira Guirguis, Mire Zloh and Jacqueline L. Stair, 257, 
Chapter 10 Light in Forensic Science: Microcrystalline Tests of New Psychoactive Substances Using Light Microscopy M. Baron, L. Elie, M. Elie and M. Vetter, 279, 
Chapter 11 Optical Detection of NPS Internet Products via HPLC-DAD Systems: A Selective Review M. G. Schmid, 301, 
Chapter 12 Supramolecular Approach in Detecting Drugs of Abuse: Optical Sensors Karl J. Wallace and J. Hugh Broome, 333, 
Chapter 13 Photodegradation of Drugs/Illicit Drugs in Water Paola Calza and Davide Vione, 371, 
Chapter 14 Photodegradation of Drugs of Abuse in Hair Giorgia Miolo and Donata Favretto, 399, 
Subject Index, 423, 

CHAPTER 1

Light for Crime Scene Examination

Valerio Causin and Giuseppe Guzzini

Table of Contents
1.1. Introduction 3
1.2. A Brief Summary on the Theory of Light 5
1.3. Imaging on the Crime Scene: Finding Traces 9
1.3.1. Observation in the Absorption/Reflection Mode 9
1.3.2. Fluorescence 10
1.3.3. Chemiluminescence 15
1.4. Photographic Techniques: Documenting Traces 15
1.4.1. Absorption Mode 15
1.4.2. Diffuse Reflection Mode 19
1.5. The Lab-on-the-scene Approach 22
1.6. Conclusion 23
References 24

1.1. Introduction

Forensic science is a very powerful investigative tool, irreplaceable in many instances for the elucidation of complex cases and for an objective understanding of the dynamics of criminal acts. Looking back at the history of forensic science, every time a new technique became available for acquiring data on the crime scene, a disruptive step forward was introduced in the ability of police forces to identify and prosecute criminals and eventually to fight crime. This was especially true at the end of the 19th century when the first studies on fingerprints as means for the identification of individuals were published by Faulds and Galton. Just a few years had elapsed from these seminal works when, in Argentine in 1892, Juan Vucetich was the first to solve a criminal case using fingerprints for the identification of a felon. This started the era of modern forensic science. An equally revolutionary advancement came with the development of DNA typing, in 1985.3 Since then, more and more sensitive techniques have been devised, decreasing the minimum sample size for obtaining a reliable DNA profile. Less than 30 years later, it is almost impossible to imagine investigation without DNA. Technology and science are shaping and enhancing the ability of forensic science to achieve its purpose, i.e. the study of traces related to crimes. Traces can be defined as the remnants of an activity and forensic science endeavours to deduce from the traces left on the crime scene as much information as possible on the crime itself. This concept is very well synthesised by the well known Locard's principle, which is often defined as 'every contact leaves a trace' even though Locard himself never formulated such an expression. Locard's words are very effective in stating this basic concept:

it is impossible for a criminal to act, and especially to act with the intensity that a crime requires, without leaving traces of his presence. This was later elaborated introducing the notion that traces can be evidence left by the felon on the crime scene, but also, for a reverse action, they can be items collected from the crime scene and transferred to the felon.

Kirk very fittingly formulated the definition of traces as mute witnesses:

wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as a silent witness against him. Not only his fingerprints or his footprints, but his hair, the fibers from his clothes, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen he deposits or collects. All of these and more, bear mute witness against him. This is evidence that does not forget. It is not confused by the excitement of the moment. It is not absent because human witnesses are. It is factual evidence. Physical evidence cannot be wrong, it cannot perjure itself, it cannot be wholly absent. Only human failure to find it, study and understand it, can diminish its value.

From this short historical introduction, it should clearly emerge that traces and the Locard's principle are foundation stones without which forensic science would not exist. Acknowledging that the purpose of forensic science is interrogating material remnants of a criminal activity provides a theoretical and philosophical framework for implementing science into the administration of justice in the most effective way. Differently to what appears in fiction, the role of the forensic scientist, in fact, is not to determine if the suspect is guilty or not, but it is to reconstruct as precisely as possible the chain of events associated to a crime, giving to the Court, to the investigators or to the lawyers reliable information to properly do their job.

In such a context, if contact is always accompanied by the transfer of some material, then the analysis and characterisation of such material can allow the forensic scientist to describe, prove or confirm the contact that originated it. Of course, such a logical path will have a successful outcome depending on a number of non-negligible factors. Transfer, persistence and recovery are the three main processes that, if successful, allow the trace, and especially the information associated with it, to reach the laboratory and eventually the Courtroom. In other words, traces must be transferred onto the crime scene or to the felon, they must remain on the crime scene or on the felon, and they must be found and retrieved from the crime scene or from the felon. This latter step is a considerable bottleneck in the process. Transfer and persistence depend on the dynamics of the crime, they are not related to the training or ability of investigators or scientists. However, if suitable procedures are not applied in the search and recovery of the items from the crime scene, there is a severe risk that some important information is lost or that contamination is introduced. In both cases, the work of investigators would be hindered rather than aided by forensic science. The fragility, the lability, the latency and the corruptibility of traces calls for highly qualified personnel operating on the crime scene, because any mistake made in this phase will jeopardise all the subsequent analyses and interpretation.

Crime scene investigation started as the set of procedures aimed at crystallising the crime scene and at describing it. Ottolenghi, a pioneer in forensic sciences in Italy, in the early 1900's, extended the concept of Bertillon's portrait parlé, which was used for giving an objective description of individuals, to the crime scene. Just as a detailed description of the physical features of a person can bring to a non-ambiguous identification, a careful depiction of the crime scene can give investigators and all those involved in the judicial process a solid foundation on which the verification of crimes and the search for the perpetrators can be developed.

If on one hand crime scene examination started as a mere descriptive activity, the modern implementation of such a critical step of forensic science includes the proactive search for items, the screening of the traces and the application of field tests.

Even though the number of texts dedicated to crime scene examination is much lower than forensic science books, most police forces and supernational bodies, such as European Network of Forensic Science Institutes, publish guidelines or best practice manuals, sometimes available on their websites. It is not the purpose of this chapter to describe the technicalities of crime scene investigation, such as how to approach the crime scene, how to move around it and how to collect and store evidence. For such details, the interested reader is referred to the specialised literature. And to the aforementioned guidelines and best practice manuals.

As anticipated above, crime scene examination is a set of analytical activities aimed at searching, collecting and preserving all the elements which, either per se or, even more importantly, due to their spatial location, can be considered evidence useful for the reconstruction for the dynamics of a crime and for identification of the perpetrators. The contextualisation of the items is therefore a fundamental element for attributing evidential value to a trace. The operator is not a mere gatherer of items, but is rather a specialist with a strong forensic background which can guide him towards an educated evaluation of traces and of their interrelationship. This is especially relevant in equivocal cases of death, in crimes perpetrated in a domestic context, or in cases of staged or simulated crime scenes, in which the significance of each trace is not due to the nature of the trace itself, but on its coherence with the possible hypotheses which can be set forth on the dynamics of the event.

Differently from what TV shows and fictional literature suggests, crime scene investigators are humans, and as such rely on their senses for searching and examining traces. Our eyes, though, have a limited sensitivity and much information would be lost both because it is too small to be detected in the chaos of a crime scene and because it is latent and invisible to the naked eye. The purpose of this chapter is to review the technical approaches which can be followed for widening the human senses and thus make the search for traces on a crime scene more effective and more productive.

1.2. A Brief Summary on the Theory of Light

As will emerge more clearly later in this chapter, exploiting the interactions between light and matter is a very effective method to detect latent traces and to find information on a crime scene.

Light is electromagnetic radiation, i.e. it is radiant energy which propagates as a wave. The features which define a wave are the wavelength, ?, i.e. the distance between adjacent crests or troughs, or the frequency, v, i.e. the number of cycles passing by a fixed point per unit time (Figure 1.1).

Frequency is also a very important parameter because it is related to the energy of the electromagnetic radiation by the well known relationship E = hv, where E is the energy of the photon and h is the Planck constant, 6.62 × 10-34 J s. In other words, the higher the frequency, the greater the energy of the radiation. For practical and historical reasons, the electromagnetic spectrum, i.e. the set of all the possible radiations, has been broken down in several regions according to wavelength (Figure 1.2), even though the physical behaviour of electromagnetic radiation does not change as a function of frequency or energy.

The human eye is only sensitive to the visible range, a quite small portion of the whole electromagnetic spectrum with wavelengths comprised between 380 and 780 nm, which is a significant limit in the field of crime scene examination, where a number of traces remain latent when examined with this light. It should also be kept in mind that the sensitivity of the human eye is not equal for all the wavelengths of the visible range, but has a maximum for green, and decreases significantly towards red and blue/violet. The use of detectors rather than the naked eye, when working with these wavelengths, can significantly improve the chances of success in the search for tiny traces. Other useful portions of the electromagnetic spectrum, inaccessible to the human eye, but easily detectable with suitable technologies, are the near ultraviolet radiation, which is more energetic than visible light and has wavelengths from 200 to 380 nm, and the near infrared region, with a lower energy than the visible light and wavelengths comprised between 0.78 and 2.5 µm.

Before proceeding with the various observation techniques which may be useful during the examination of a crime scene, it may be useful to summarise the different phenomena which may happen when light interacts with matter. The discussion will focus on a reflection geometry of illumination, because in most of the practical instances the traces observed are opaque, and not transparent.

When light containing all the visible wavelengths (white light) impinges an object, the object will absorb only certain wavelengths, whereas unabsorbed wavelengths will be reflected. These latter wavelengths will be perceived as a colour (Figure 1.3).

The colour seen will be the complementary colours to the absorbed colours. Figure 1.4 shows the "colour wheel", colours that are opposite on the wheel are complementary.

In other words, the object will absorb some of the colours contained in white light, allowing only the unabsorbed hues to be reflected back and to reach the eye of the observer. In our daily life we are very familiar with the absorption of visible light and the vision of colours, but the same physical phenomenon happens when the impinging light is from other regions of the electromagnetic spectrum, e.g. ultraviolet or infrared light.

Scattering is another phenomenon which may happen when an object is illuminated with light. When the wavelength of incoming light is comparable with the size of the illuminated objects, these start vibrating with the same frequency of light and they themselves become spherical sources of radiation. When this happens, some of the light is diffused at 360° around the object, blurring the purely geometrical propagation of light. In fact, when light interacts with smooth and shiny surfaces the radiation is reflected, with respect to the perpendicular to the surface, with an angle which equals the angle of incidence (Figure 1.5a). This mode is called specular reflection. In contrast, if light encounters a rough surface, scattering occurs, and it is reflected in all directions of space, diffusing the radiation in the surrounding space (Figure 1.5b). In such case, the phenomenon is called diffuse reflection.

Fluorescence is a further phenomenon which is very useful for detecting traces. When a molecule absorbs light, it absorbs energy which is used to promote electrons to an excited state. Disexcitation may happen by the re-emission of light of the same wavelength, with a concurrent return of the electrons to their ground state. However, an alternative mechanism, called fluorescence, exists, in which some non-radiative decays, i.e. processes in which energy is lost without emission of radiation, accompany the return to the ground state by emission of light. In other words, when fluorescence happens, a compound absorbs light of a particular wavelength and energy, and re-emits radiation with a longer wavelength and lower energy. Many biological traces display fluorescence, which therefore is a very efficient method for their detection.

1.3. Imaging on the Crime Scene: Finding Traces

1.3.1. Observation in the Absorption/Reflection Mode

A crime scene is a very complex environment, in which traces with an evidential value coexist with a large number of items which do not carry any significant information of the event. Moreover, traces are often tiny, sometimes the perpetrator tries to erase them, and thus their detection is not easy. Finally, many kinds of traces are not directly visible to the naked eye, because they are not coloured and/or because they have a similar colour to the background surface where they lay. The purpose of the crime scene investigator is therefore to enhance, as much as possible, the contrast between the trace and the background, in order to clearly visualise it, aiding both its detection, documentation and retrieval.

As mentioned above, the human eye has a sensitivity limited to the visible range, and within this wavelength region it is more effective in detecting green rather than red or violet.

A white light source is certainly suitable for a first survey of the scene, for detecting the most evident traces. However, the diversity of materials, in different colours and with different surface roughness, which can be encountered on crime scenes, calls for the application of more sophisticated approaches, if one wants to avoid missing important pieces of information.

In the first instance, absorption can be exploited to improve contrast. Using an illumination source of the same colour as the surface, the background will appear much lighter, and stains or traces on it will be dark features. An alternative to this could be illuminating with a colour complementary to that of the surface, which will appear dark, whereas traces should stand out as lighter features.

The choice of the illuminating wavelength also depends on the particular type of trace which the investigator is looking for. For example, the UV-visible spectrum of blood shows a prominent absorption peak at 415 nm. If a blood spattered surface is observed with monochromatic light with this wavelength, the blood spots will appear as dark regions, because they will absorb all the radiation impinging upon them. If the surface does not absorb at 415 nm, or even if it reflects a portion of it, the substrate will lighten up, improving the contrast of the image. This can be practically performed with commercial tunable-wavelength light sources if working in dark conditions, or by illuminating with white light and observing through a filter at 415 nm.

(Continues...)

Excerpted from Light in Forensic Science by Giorgia Miolo, Jacqueline L. Stair, Mire Zloh. Copyright © 2018 European Society for Photobiology. Excerpted by permission of The Royal Society of Chemistry.
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Edition details

• Publisher: Royal Society of Chemistry
• Publication date: 2018
• Language: English
• ISBN 10: 1782627685
• ISBN 13: 9781782627685
• Binding: Hardcover
• Edition number: 1
• Number of pages: 448
• Editor: Giorgia Miolo