Kirk's 'Ontogeny of Criminalistics' revisited under the lens of the Sydney Declaration

The present commentary reviews the considerations of the famous American criminalist Paul Kirk in his seminal publication of 'The Ontogeny of Criminalistics,' written sixty years ago, regarding the status of forensic science and its fundamental principles. Professor Kirk aimed to examine forensic science as an independent scientific discipline, resulting in the identification of six key topics: 1) The need for fundamental principles; 2) the distinction between 'identification' and 'individualization;' 3) the qualifying elements of a profession; 4) the qualifying aspects of a science; 5) the need for a research-oriented basis; 6) the need for application of statistics and probability. In particular, Kirk deemed the nature of the progress made during his time as technical, practical, and transient at the cost of being fundamental, theoretical, and permanent. Predominantly, it is still the case today, with a post-effect fragmentation of forensic science into a myriad of ultra-specialized subdisciplines and applications. The lack of proper articulation of the most fundamental principles of forensic science was one of Kirk's most pressing concerns. The Sydney Declaration aimed to recapture the current fundamental (ontological and epistemological) status of forensic science, resulting in the redefinition of forensic science and its prime object of study, the trace, and in the consolidation of seven principles. The present commentary attempts to address Kirk's arguments in the Ontogeny in the context of the principles of the Declaration, with particular emphasis on the fundamental principles as well as Kirk's distinction between 'identification' and 'individualization,' which is considered critical to understanding the overall scope of forensic science.

Suspected serial killers and unsuspected statistical blunders

A whole branch of theoretical statistics devotes itself to the analysis of clusters, the aim being to distinguish an apparent cluster arising randomly from one that is more likely to have been produced as a result of some systematic influence. There are many examples in medicine and some that involve both medicine and the legal field; criminal law in particular. Observed clusters or a series of cases in a given setting can set off alarm bells, the recent conviction of Lucy Letby in England being an example. It was an observed cluster, a series of deaths among neonates, that prompted the investigation of Letby. There have been other similar cases in the past and there will be similar cases in the future. Our purpose is not to reconsider any particular trial but, rather, to work with similar, indeed more extreme numbers of cases as a way to underline the statistical mistakes that can be made when attempting to make sense of the data. These notions are illustrated via a made-up case of 10 incidents where the anticipated count was only 2. The most common statistical analysis would associate a probability of less than 0.00005 with this outcome: A very rare event. However, a more careful analysis that avoids common pitfalls results in a probability close to 0.5, indicating that, given the circumstances, we were as likely to see 10 or more as we were to see less than 10.

Bloodstain pattern analysis & Bayes: A case report

The findings from a bloodstain pattern analysis (BPA) may assist in formulating or falsifying scenarios that are considered in the investigative stages of a criminal investigation. When a case proceeds to trial the bloodstain pattern expert may be asked about the relevance of their findings given scenarios that are proposed by the prosecution and defense counsel. Such opinions provided by an expert are highly relevant to police investigation or legal proceedings, but the reasoning behind the opinion or implicit assumptions made by the expert may not be transparent. A proper framework for the evaluation of forensic findings has been developed since the late twentieth century, based on the hierarchy of propositions, Bayesian reasoning and a model for case assessment and interpretation. This framework, when implemented in casework, mitigates some of the risks of cognitive biases, and makes the reasoning and scientific basis for the opinion transparent. This framework is broadly used across forensic science disciplines. In this paper we describe its application to the field of BPA using a case example from the Netherlands Forensic Institute (NFI).

The logic of forensic pathology opinion

Evaluating evidence and providing opinions are at the heart of forensic science, and forensic experts are expected to provide opinions that are based on logically sound and transparent scientific reasoning, and that honour the boundaries of their area of expertise. In order to meet these objectives, many fields of science explicitly apply Bayes' theorem, which describes the logically correct way to update probabilities on the basis of observations. Making a distinction between 'investigative' and evaluative' modes of operating helps to implement the theorem into daily casework. Use of these principles promotes the logic and transparency of the reasoning that leads to expert's opinion and helps the expert to stay within her remit. Despite these important benefits, forensic pathology seems slow to adopt these principles. In this article, we explore this issue and suggest a way forward. We start with a short introduction to Bayes' theorem and its benefits, followed by a discussion of why its application is actually second nature to medical practitioners. We then discuss the difference between investigative and evaluative opinions, and how they enable the forensic pathologist to reconcile Bayes' theorem with the different phases of a forensic investigation. Throughout the text, practical examples illustrate the various ways in which the logically correct way of evidence interpretation can be implemented, and how it may help the forensic pathologist to provide an appropriate and relevant opinion.

Forensic soil analysis using laser-induced breakdown spectroscopy (LIBS) and Fourier transform infrared total attenuated reflectance spectroscopy (FTIR-ATR): Principles and case studies

Soils are crucial trace evidence that can establish or exclude the relationship between a suspect, victim, or an object at a particular scene, which could contribute to building a case. Laser-induced breakdown spectroscopy (LIBS) and Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy have been demonstrated to be effective techniques for soil characterization owing to its being rapid, non-destructive, and convenient analysis with little sample preparation requirements. Therefore, the principles of LIBS and FTIR-ATR techniques for soil forensic analysis in typical soil samples were investigated and their practical feasibility was tested by applying the techniques to forensic soil samples in two criminal cases. Principal component analysis (PCA) of a typical soil sample indicated that five typical soil types were clearly distinguished by LIBS and FTIR-ATR spectra. Variations in the soil elements (i.e., Si, Mg, Al, Ca, K, O, and N) and functional groups (i.e., OH/NH, CC/CO, SiO, CO₃^2-, AlOH, and NH₂) are crucial indicators for soil identification. The casework results demonstrated that both LIBS and FTIR-ATR show great potential for forensic soil analysis in future cases.

Sharing data on DNA transfer, persistence, prevalence and recovery: Arguments for harmonization and standardization

Sharing data between forensic scientists on DNA transfer, persistence, prevalence and recovery (TPPR) is crucial to advance the understanding of these issues in the criminal justice community. We present the results of a collaborative exercise on reporting forensic genetics findings given activity level propositions. This exercise outlined differences in the methodology that was applied by the participating laboratories, as well as limitations to the use of published data on DNA TPPR. We demonstrate how publication of experimental results in scientific journals can be further improved to allow for an adequate use of these data. Steps that can be taken to share and use these data for research and casework purposes are outlined, and the prospects for future sharing of data through publicly accessible databases are discussed. This paper also explores potential avenues to proceed with implementation and is intended to fuel the discussion on sharing data pertaining to DNA TPPR issues. It is further suggested that international standardization and harmonization on these topics will benefit the forensic DNA community as it has been achieved in the past with the harmonization of STR typing systems.

Applications of Raman spectroscopy in forensic science. I: Principles, comparison to infrared spectroscopy, and instrumentation

There have been several significant advances in Raman spectroscopy instrument technology during the past few decades, including the introduction of several new laser sources, the development of holographic gratings, efficient Rayleigh line rejection filters, and CCD array detectors, and the advent of FT-Raman spectrometers. In view of these developments, Raman spectroscopy is now a fully mature analytical technique on par with its counterpart, infrared spectroscopy. The latter technique experienced a quantum leap in use in the forensic science laboratory following the introduction of inexpensive FT-IR spectrometers in the 1980s, but forensic scientists have been slower to embrace Raman spectroscopy. This may stem in part from the perception that fluorescence prevents its use for many samples. However, a more significant factor may be insufficient understanding of the unique capabilities of Raman spectroscopy, including how it can provide information not accessible using other methods. This promising technique is finally making some inroads into the forensic science laboratory, and this will continue as forensic scientists gain a greater appreciation of its features and merits. To facilitate this process, this article presents a comprehensive review of Raman spectroscopy, with an emphasis on how and why this underutilized cousin to infrared spectroscopy can be a very valuable tool for the analysis of a wide variety of evidentiary materials. Owing to the wide scope of this review, it is presented in two parts. Most forensic scientists are not very familiar with inelastic scattering and Part I of this article describes the principles and instrumentation of Raman spectroscopy. Forensic scientists, however, are generally more knowledgeable about infrared spectroscopy, and a comparison of the spectral data produced by these two related vibrational methods for various categories of analytes is also presented and discussed.

Applications of Raman spectroscopy in forensic science. II: Analysis considerations, spectral interpretation, and examination of evidence

There have been several significant advances in Raman spectroscopy instrumentation during the past few decades, and this method is now a fully mature analytical technique on par with its counterpart, infrared spectroscopy. The latter method experienced a quantum leap in use in the forensic science laboratory following the introduction of inexpensive FT-IR spectrometers in the 1980s, but forensic scientists have been slower to embrace Raman spectroscopy. However, this promising technique is finally making some inroads into the forensic science laboratory, and to facilitate this process, this article presents a comprehensive review of Raman spectroscopy; it emphasizes how and why this underutilized method can be a very valuable tool for the analysis of a wide variety of evidentiary materials. Part I of this article described the principles of Raman spectroscopy, including theory, instrumentation, and a comparison of spectral data obtained using infrared and Raman methods for various analytes. Part II discusses how different analytical conditions can affect Raman spectra, and what bearing this and other factors may have on spectral interpretation; it also presents a review of the literature describing applications of Raman spectroscopy for the examination of various types of evidence.

Surface enhanced Raman spectroscopy: A review of recent applications in forensic science

Surface enhanced Raman spectroscopy has many advantages over its parent technique of Raman spectroscopy. Some of these advantages such as increased sensitivity and selectivity and therefore the possibility of small sample sizes and detection of small concentrations are invaluable in the field of forensics. A variety of new SERS surfaces and novel approaches are presented here on a wide range of forensically relevant topics.

Estimation of gestational age from gall-bladder length

Establishing a precise duration of gestation is vital in situations such as infanticide and criminal abortions. The present study attempted to estimate the gestational age of the foetus from gall-bladder length. Foetuses of various gestational age groups were dissected, and the length of the gall bladder was measured. The results were analysed, and a substantial degree of correlation was statistically confirmed. This novel method is helpful when the foetus is fragmented, putrefied or eviscerated, where this method can be used as an additional parameter to improve the accuracy of foetal age estimation.

Contemporary Sample Preparation Methods for the Detection of Ignitable Liquids in Suspect Arson Cases

The isolation of ignitable liquid components, usually petroleum-based distillates from fire debris, is an important step in deciding whether a fire is of natural or incendiary origin. Steady progress has been made to develop sample preparation methods capable of enriching target analytes in high yield and within a short period of time. Heated headspace enrichment methods are currently most widely used. There are several variations of this basic technique. Carbon-based adsorbents are most popular. They come in different forms and shapes, including a flat sheet of polymer, impregnated with carbon particles. The analyst cuts a small strip from this sheet and suspends it in the heated headspace above the debris sample. The volatiles adsorb onto the carbon surface, eventually reaching an equilibrium condition. The process is usually carried out in an oven. This convenient method, called the static method, has largely replaced the dynamic method, which uses a granular charcoal adsorbent. In the latter, the heated headspace is drawn over a short trap packed with charcoal, using a source of vacuum such as a pump or pushed along using pressurized nitrogen. The headspace volatiles in both the static and dynamic method are recovered by elution with a solvent, usually carbon disulfide. Recently, a promising variation of the static headspace method has been introduced. It is based on the use of a tiny amount of a polysiloxane polymer which has been coated onto the tip of a thin silica fiber. The fiber can be retracted into a syringe-type needle and the adsorbed headspace vapor can be conveniently introduced into the heated injector port of a gas chromatograph. No solvent is required. This technique, abbreviated SPME (for solid-phase microextraction) has many attractive advantages but it is not without some problems. Low boiling range accelerants, including water-soluble polar substances such as ethanol, are poorly retained on methylsiloxane type polymers. The recent introduction of hybrid fibers containing a combination of carbon and a methylpolysiloxane polymer has extended the usefulness of SPME toward the high volatility end. With judicious optimization of experimental conditions, it is now possible to obtain an adequately representative sample of the headspace above the fire debris sample. It is thus possible to characterize the full spectrum of potential liquid accelerants, ranging from alcohols and similar water-soluble substances to high boiling range fuel oils.