Until the nineteenth century, the use of chemicals to murder someone without a trace was very common due to the absence of the analytical methods needed to test and prove the poisoning. In addition, many symptoms of chemical poisoning are very similar to those of some natural diseases. Arsenic, for example, is one of the chemicals frequently used to poison; its detection, based on chemical sensing, is one of the landmarks of Forensic Analytical Chemistry.

During a trial, a judge could consider an expert witness’s opinion of crime evidence as a fact until the court reached a verdict. In 1832, John Bodle, who was accused of murdering his grandfather by using arsenic, was put on trial in London.¹  James Marsh, a British chemist appointed as an expert witness in this trial, tried to detect arsenic in the grandfather’s stomach. Using the hydrogen sulfide test,²  Marsh detected arsenic as the evidence of the crime. However, the test result degraded before it could be shown to the jury. While Bodle could not be found guilty of his grandfather’s murder, he later confessed to the crime after the jury verdict. Due to this outcome, Marsh began the research to propose a reliable test that could prove arsenic poisoning in biological tissues and could therefore be used as evidence to show a jury.

In the four years following the Bodle trial, Marsh worked hard to develop a reliable test that could be used as evidence to prove someone’s guilt in a courtroom. To achieve this goal, he set out to improve Carl Wilhelm Scheele’s test which was used to detect the existence of arsenic.³  Scheele’s method mixed arsenic powder with metallic zinc and nitric acid. This mixture was then heated, releasing the garlic aroma of arsine gas (AsH₃), which could be detected by someone. However, just like the hydrogen sulfide test used by Marsh in the Bodle case, the positive result was unreliable and could not be used in court. Hence, Marsh proposed using the ternary mixture of the Scheele’s test, reaction (1). When the arsine gas was formed, he confined the gas in a funneled tube, and heated the tube again, reaction (2). The trapped arsine gas decomposed into a gray metallic film, forming an “arsenic mirror” that could be used as evidence in the courtroom.⁴ 

The pioneering use of the Marsh’s test as a forensic tool in a trial to prove guilt occurred in 1840 during the infamous Marie LaFarge case. In brief, the widow was accused of murdering her husband, Charles Lafarge, by adding arsenic to his food and drink. The positive test result for arsenic using Marsh’s procedure started the process which sent her to prison.⁵  The Lafarge trial was a landmark for the use of chemical sensing tests and analytical methods in murder trials, ending the impunity of poisoning cases and allowing decisions to be made in forensic cases. Hence, the development of analytical methods and the use of analytical techniques occupies an important place in modern criminal investigation, as these methods will be the tools used to detect and quantify chemicals in crime scene investigations. Currently, most analytical laboratory methods use sophisticated techniques, such as atomic absorption spectrometry (AAS)⁶  and inductively coupled plasma mass spectrometry,⁷  to detect, for example, arsenic in a biological sample. However, a new analytical method mentioned in the literature needs to be well-established or needs to meet some additional criteria before being used in court to be recognized as a Frye standard in the forensic field.

The Frye standard originates from Frye vs United States,⁸  where the systolic blood pressure deception test was used as evidence to indicate if someone was telling the truth based on a change in their blood pressure. The US made two important statements in this document:⁸ 

These statements show that the analytical methods or techniques need to be recognized by the scientific community before they can be used as evidence in trials. However, the real change in the criteria for the admittance of scientific analytical method evidence occurred with the Supreme Court’s 1993 decision in Daubert vs Merrell Dow.⁹  This case recognized five factors that a judge could ponder in the evaluation of an analytical method being used in a court. These factors are: “(1) whether the theory or technique can be (and has been) tested; (2) whether the theory or technique has been subjected to peer review and publication; (3) the known or potential rate of error of a particular scientific technique; (4) the existence and maintenance of standards controlling the technique’s operation; and (5) a scientific technique’s degree of acceptance within a relevant scientific community”.¹⁰ 

Hence, as reported by Hark and East,¹¹  “the provisions of the Daubert standard not only establish guidelines for the introduction of new methods of forensic analysis, they also form the basis for challenging some long-accepted techniques in court.” This incorporates the Frye standards.

Based on this approach, some analytical techniques that can be considered for the analysis of evidence were reported by Hark and East¹¹  (Table 1.1).

All techniques reported in Table 1.1 have met the Daubert standard requirements as previously mentioned. One of the last techniques included in this list as a standard technique for crime scene investigation was the LIBS (Laser-Induced Breakdown Spectroscopy). LIBS was included after none of the other well-known techniques could be used to solve a murder of a child by a woman as reported by the news in Orlando, USA, in 2008.¹²  The criteria presented in the Daubert standards were used to find the legitimacy of the LIBS technique to evaluate the evidence found in the car trunk’s carpet. Researchers from Oak Ridge National Laboratory demonstrated that the elementary behavior of some elements like Ca, Mg, and Na found in the carpet was similar to the behavior reported by a model that simulates the putrefaction progression of a body. This evidence was accepted by the court in the woman’s trial. Hence, one of the main purposes of this book is to describe the fundamentals and the forensic applications of these well-known analytical techniques in courts and trials.

Various techniques, such as electrochemical methods, that could be used in the future to investigate forensic samples will also be discussed in this book. Additionally, portable techniques could be very helpful in on-site crime scene investigations. Any increase in the amount of evidence collected increases the number of definitive sample analyses. Fast and accurate in-field tests are extremely important to decrease the number of definitive analyses.^13,14  To be practical, these analyses must be simple and specific. This point-of-need analysis for forensic applications makes these tests widely used as a first step to analyze some materials, such as illicit substances, as it is not necessary to store a large volume of samples for a standard method. The principle and application of these methods will be discussed in this book as well.

This book will also examine new techniques that study the use of DNA methylation for forensic sciences. These techniques provide great potential to aid forensic applications by permitting investigators to track variations in gene expression in crime scene analysis. Epigenetic procedures have the potential to offer a whole new level of specificity in forensic body fluid analysis and the detection of these differences by epigenetic methods permits a more specific and sensitive technique to detect human cells left behind by suspects at crime scenes like identification a suspect’s age, lifestyle, and diet, resulting in a new future tool for crime scene investigations.

Finally, the importance of proper sampling technique and sample preservation prior to the analysis by a standard method will be discussed as well. One example, in particular, is the O. J. Simpson case reported in the media.¹⁵  While the standard analytical method had the required accuracy as well as the five Daubert criteria needed to allow its use in the court, Mr. Simpson was not found guilty due to problems with sampling collection contamination at the crime scene.