Many textbooks are currently available concerning crime scene examination and the forensic analyses of the material recovered from the crime scene, covering a large range of techniques and approaches.

The peculiarity of this book is that it is specifically targeted at light-based instrumental methods and at light of specific wavelengths for gathering evidence in the crime scene, assessing a number molecules useful in the crime scene solving and, at the same time, it presents the adverse photodegrading effects of light on materials of interest.

Since many traces are invisible to the naked eye, various types of illumination and visualisation techniques are devised in order to aid the activity of the examination teams.

The book covers the analysis of a range of molecular systems for forensic examination purposes, with a detailed review of different analytical methods that use light sources for either illumination or detection of trace samples, including illicit drugs and novel psychoactive substances (NPS), biological agents that may be used in bioterrorism, polymeric material, i.e. fibres, reflectors, adhesive tapes, textiles, and glass materials with a particular emphasis on detecting, analysing and interpreting evidence from crime scenes.

This book contains chapters with a review of such approaches, based on absorption, scattering and reflection of light of different wavelengths, and on the exploitation of fluorescence and chemiluminescence.

Moreover, the accurate and rapid identification of bacteria using laser irradiation via MALDI-TOF MS is widely discussed in a chapter dedicated to this methodology for detection of biological warfare agents.

Spectroscopic techniques are ideal tools for detecting analytes at trace levels i.e., low concentrations. Microspectrophotometry, Raman spectroscopy, FTIR spectroscopy, IR-chemical imaging and X-ray fluorescence spectroscopy are also discussed as recommended tools to determine the nature, class and subclass of polymers, such as fibers.

In regards to glass evidence, this has the ability to provide information not only to link individuals to broken glass items found at a crime scene but also to help establish what, when and how these were transferred. In this context, light plays a fundamental role in obtaining particularly source information, because the morphology, optical and chemical properties of glass can be characterised by different regions of both the visible and near visible electromagnetic spectrum.

In contextual chapters, NPS and illicit drugs' detection by light based techniques and the possibility of photodegradation in different matrices (both in water from various sources for epidemiological studies and in in vivo samples, i.e. hair of potential consumers) are extensively discussed and will provide the reader with a solid background in this area of crime investigation.

Normally, at a crime scene the evidence needed is often obtained by collecting the analytes of interest and the samples are often taken back to the lab for analysis. Nevertheless, there has been a recent surge in portable methods that can be used at the site of the crime or in emergency rooms. Supramolecular host-guest systems, providing the necessary architecture for portable systems while being cost effective, selective and sensitive, are described in a specific chapter of this book, focusing on the recognition of drugs of abuse that utilise optical changes i.e., changes in colour or fluorescence response.

Furthermore, a chapter is dedicated to Raman spectroscopy which has been shown to decipher NPS chemical analogues as well as the NPS from cutting agents and adulterants present in associated products. Analysis can be done in the laboratory or in-field using handheld versions, in which the latter often have in-build matching algorithms for a quick response for non-experts.

Additionally, many synthetic novel psychoactive compounds contain a stereogenic centre leading to two possible enantiomers, whose pharmacological potency differs as it is the case for many chiral active pharmaceutical ingredients. Therefore, the analytical methods for enantioseparation of NPS by high performance separation techniques (HPLC, capillary electrophoresis, capillary electrochromatography and supercritical fluid chromatography) with UV absorption detection is of great forensic interest.

Another chapter is dedicated to hair analysis as a valuable tool in forensic toxicology to demonstrate drug exposure in the context of facilitated crimes. Since scalp hair is exposed to sunlight and/or artificial light for many hours per day; the action of light on hair could alter the content of drugs/illicit drugs and/or metabolites and the xenobiotics can gradually disappear or be transformed into other compounds. Thus, light exposure should be considered as a potential confounder in studies investigating xenobiotics in hair giving rise to reduced drug concentrations or even false negative results.

Indeed, the second aspect of the light discussed in this book concerns the degrading effects of light, both induced by the analytical methods employed (i.e. UV light breakage of DNA during DNA profiling) or by sunlight when outdoor samples are collected and then subjected to forensic analyses.

Moreover, the current processes used in the forensic analysis of DNA and RNA are covered in a selected chapter detailing why light is essential for detection but also destructive to the template DNA collected during a criminal investigation.

When traces have been exposed for long periods of time to weathering, degradation, especially by light, can modify their structure and complicate the work of the analyst. The issues related to degradation of material evidence found at the crime scene are discussed, focusing also on polymeric evidence, because polymers are the traces most sensitive to degradation, whereas glass or soil are not significantly changed by exposure to light for the time durations usually involved in normal casework.

At the same time the adverse effects of light on materials of interest as evidence could open opportunities for development of additional markers not yet explored or yield an enrichment of libraries for dedicated instruments by adding degradation products to reduce false negative or positive results.

In conclusion, this book aims to cover the latest research and development based on light methodologies in the crime scene investigation by specialists from forensic institutions and departments worldwide. Indeed, as light can play a powerful role in this environment, the presented material will allow reader to gain in depth understanding on how the light affects the evidence and when to apply techniques that employ light for crime scene investigations.

Giorgia Miolo, Jacqueline L. Stair and Mire Zloh