On the use of IRMS in forensic science: proposals for a methodological approach

The flourishing number of publications on the use of isotope ratio mass spectrometry (IRMS) in forensic science denotes the enthusiasm and the attraction generated by this technology. IRMS has demonstrated its potential to distinguish chemically identical compounds coming from different sources. Despite the numerous applications of IRMS to a wide range of forensic materials, its implementation in a forensic framework is less straightforward than it appears. In addition, each laboratory has developed its own strategy of analysis on calibration, sequence design, standards utilisation and data treatment without a clear consensus. Through the experience acquired from research undertaken in different forensic fields, we propose a methodological framework of the whole process using IRMS methods. We emphasize the importance of considering isotopic results as part of a whole approach, when applying this technology to a particular forensic issue. The process is divided into six different steps, which should be considered for a thoughtful and relevant application. The dissection of this process into fundamental steps, further detailed, enables a better understanding of the essential, though not exhaustive, factors that have to be considered in order to obtain results of quality and sufficiently robust to proceed to retrospective analyses or interlaboratory comparisons.     

Application of aspartic acid racemization to forensic odontology: post mortem designation of age at death

The extent of racemization of aspartic acid in the dentin of healthy, carious and impacted teeth was used to define the ages of individuals at the time of their death. These determinations were performed with an error of +/- 4 years. This method holds the promise of simplifying procedures in, and extending the application of forensic odontology. The current error range of this method may be reduced by analyzing teeth of the same positional types from deceased individuals of known age. Using this method, it appears that post mortem preservation of up to 10 years has a negligible effect on the values determined for the age of individuals at death.     

Geomatic techniques in forensic science: A review

The purpose of this review paper is to highlight various geomatic techniques that crime scene reconstructionists or forensic practitioners can use to document different kinds of scenes, highlighting the advantages, disadvantages, and when best to use each technology. This paper explores geomatic techniques such as a total station, photogrammetry, laser scanners and structured light scanners and how they can be used to reconstruct crime scenes. The goal of this paper is not to discredit manual methods, as they are long standing and reliable, but instead to shed light on alternative methods that may produce equally or more accurate results with a more visually appealing final product. It is important for law enforcement and forensic professionals to understand the advantages and disadvantages of each technique, knowing when certain techniques should be used (and when they should not), and being able to revert to traditional methods if required.     

Decision analysis in forensic science

Forensic scientists are routinely faced with the problems of making decisions under circumstances of uncertainty (i.e., to perform or not perform a test). A decision making model in forensic science is proposed, illustrated with an example from the field of forensic genetics. The approach incorporates available evidence and associated uncertainties with the assessment of utilities (or desirability of the consequences). The paper examines a general example for which identification will be made of the decision maker, the possible actions, the uncertain states of nature, the possible source of evidence and the kind of utility assessments required. It is argued that a formal approach can help to clarify the decision process and give a coherent means of combining elements to reach a decision.     

Age estimation from aspartic acid racemization of root dentin by internal standard method

In this study, we investigated the application of the internal standard method to determine age from aspartic acid (Asp) racemization. D-Methionine (D-Met) and D-norleucine (D-Nleu) were tested as internal standards for the purpose of validating the derivatization and gas chromatographic measurements. Using a set of standard amino acids plus the internal standards in constant volume, calibration plots with reasonable linearity (R > 0.98) were constructed. Based on the analysis of sample chromatograms, D-Met appeared to meet the criteria for internal standards, hence it was selected for use in D- and L-Asp quantification. The correlation between dentin age and D-/L-Asp ratios from the peak areas as well as from the absolute concentrations was investigated. Correlation coefficients were calculated as 0.98 and 0.90, respectively. The slight decrease in accuracy was attributed to the conversion of D-Asp/D-Met ratios to concentrations employing the calibration curves figured from pure Asp. Because the application of the internal standard method produced reproducible and precise measurements, the employment of internal standards in age estimation based on Asp racemization appears to provide quality assurance by avoiding possible errors arising from sample preparation.     

生物超弱发光在法医学中的研究应用展望

生物超弱发光携带着生物体新陈代谢和能量转化的信息,已成为生命学科的重要研究领域。本文回顾生物超弱发光的研究历史、特点及在医学领域的研究应用现状,展望生物超弱发光在法医学,尤其是死亡时间推测和损伤方面的研究应用前景     

Comparison of age estimated from degree of racemization of aspartic acid, glutamic acid and alanine in the femur

Aspartic acid (Asp) is generally used for estimation of age by measuring the degree of racemization. For other amino acids, however, there are few reports regarding the usefulness of the degree of racemization for the estimation of age. Accordingly, in this study using the femur (obtained from 21 cadavers) as the specimen, we measured the degree of racemization of glutamic acid (Glu) and alanine (Ala) along with Asp in the total amino acid (TAA) fraction as well as in acid-insoluble collagen-rich (IC) and acid-soluble peptide (SP) sub-fractions. We compared the degrees of racemization of each amino acid and the accuracy of the ages estimated from them. The degree of racemization and the reaction rate of racemization were ranked in the order of Asp > Glu > Ala in the TAA and IC fractions, but Asp > Ala > Glu in the SP fraction. It is noteworthy that the degrees of racemization differed between the three amino acids depending on the fraction tested. The correlation coefficient (r) between the degree of racemization and the chronological age was higher in the SP than in the TAA or IC fraction. Among three amino acids, Asp showed the highest correlation coefficient as predicted. The present study confirmed that Asp from the SP fraction is the best indicator for age estimation using racemization rates.     

Degradation of biomolecules in artificially and naturally aged teeth: implications for age estimation based on aspartic acid racemization and DNA analysis

Postmortem teeth are the most stable structures, and can be used to gain different information (age estimation, genetic data). Over long postmortem intervals (PMI), degradation processes may alter the molecular integrity and thus affect the reliability of applied molecular methods. Whereas some knowledge on the degradation of biomolecules in bone during the PMI exists, data for teeth are lacking. In particular, the impact of degradation processes in dentine on age estimation based on aspartic acid racemization (AAR) cannot be estimated yet. Hence, the molecular stability of both collagen and DNA was analyzed systematically, and their impact on the reliability of age estimation based on AAR and genetic analyses was checked. Two hundred and ten human and 59 porcine teeth were heated (90 degrees C in water) to simulate collagen and DNA diagenesis; 14 naturally aged teeth (PMI: 3 days to 1700 years) were analyzed comparatively. Peptide patterns of cyanogen bromide (CNBr)-cleaved collagen were employed as a new approach to check the collagen integrity. In the same samples, collagen yields, amino acid compositions, AAR in different protein fractions, and DNA integrity were analyzed. In heated human and porcine teeth the collagen content declined during the heating experiment. The amino acid composition in human samples was collagen-like until 12 days of heating. In naturally aged teeth, the collagen yielded from 9.5 to 15%, and no discrepancy of amino acid composition to that of modern collagen was observed. Electrophoresis of CNBr-peptides showed an altered pattern in experimentally degraded samples from day 10 on; naturally aged collagen displayed the typical collagen pattern. AAR increased in all protein fractions with increasing duration of the heating experiment; naturally aged samples displayed a slow accumulation of AAR. DNA degraded progressively, and after 32 h of heat exposure no more DNA was detectable, whereas the amplification of nuclear and mitochondrial DNA was successful up to 48 h. STR typing was reliable up to 16 h, and sex determination up to 40 h of heat exposure. In naturally aged samples of DNA quality, yield and typing success did not correlate with PMI. The data highlight a remarkable stability of collagen dental proteins. Within relevant forensic periods a postmortem rise of AAR under normal conditions is negligible, and analyses of dental DNA has a high chance to be successful. However, after large PMI and/or extreme postmortem conditions age estimation based on AAR and genetic analyses lose their reliability.     

A density gradient technique for use in forensic soil analysis

A high-density aqueous salt solution for the preparation of density gradients is presented. It has been used successfully by the authors in forensic soil analysis. It has a density range that allows for the separation of a soil specimen's heavy mineral components. It has no odor or toxic fumes, which eliminates the need to use a hood during preparation, and is far superior to the organic liquids normally used to prepare density gradients. This liquid should cause many forensic scientists to reexamine their attitudes towards using density gradients in forensic soil casework.     

Age estimation of bloodstains: a preliminary report based on aspartic acid racemization rate

This study describes an innovative application of a well-established method of age determination. The conventional method of aspartic acid racemization (AAR) is based on estimation of the d-l-aspartic acid ratio in slow turnover tissues, such as tooth tissue, to reflect the age of an individual. This method has been recently applied to age estimation in forensic investigations, and is also widely used for archeological dating of fossils. We suggest that the aspartic acid racemization method could be applied to a significant, although unresolved, forensic issue: that of bloodstain dating. Standard kinetic experiments were used to describe the characteristics of the racemization reaction in bloodstains, which were then employed to estimate the age of various samples. The soluble protein fraction of a bloodstain produced a stronger correlation between elapsed time and d-aspartic acid content than total amino acid fractions. According to our preliminary results, the time lapse after the creation of a bloodstain can be determined ex vivo by measuring the extent of aspartic acid racemization. Our analysis highlights the need for further study into the preservation and composition of bloodstains to assist in further development of this pioneering application.     

The forensic science use of reflective ultraviolet photography

Reflective ultraviolet photography has many forensic science applications particularly in child abuse, rape, homicide, and bite mark cases. The potential of this relatively simple and inexpensive procedure has not been fully explored. The procedure for its use in bite mark cases is presented.     

Neural networks in forensic science.

Neural networks were developed to study and mimic the functioning of the human brain. Humans are good at pattern recognition; the question is how good neural networks are at it, particularly with problems of forensic science interest. Simulation experiments with a type of neural network known as a Hopfield net indicate that it may have value for the storage of toolmark patterns (including bullet striation patterns) and for the subsequent retrieval of the matching pattern using another mark by the same tool for input. Another type of neural network, the back-propagation network (BPN), is useful for applications similar to those for which standard statistical methods of pattern classification can be used. This would be an appropriate approach to the matching of general component patterns, such as gas chromatograms of gasoline, or pyrolysis patterns from materials of forensic science interest, such as paint. The BPN may provide better results than statistical methods, but it is currently necessary to try both to determine which would be best for any given situation.     

The future of forensic and crime scene science. Part II. A UK perspective on forensic science education

This paper builds on the views presented by the author at 'The Future of Forensic and Crime Scene Science Conference'. Forensic science has become an increasingly prominent area of science within the last 10 years. This increasing prominence together with popularity in the subject has seen the number of undergraduate students studying forensic science related courses at UK Universities increase rapidly in just 5 years and there are no short term signs of this trend reducing. In 2005, there were 450 courses with forensic in the title offered by higher education institutes. Although the forensic community has expressed its concern that job prospects for these students wishing to pursue careers as forensic scientists will be limited numbers of students undertaking science courses have still increased. The increase in students studying forensic science comes in an era of decreasing science numbers in higher education with the potential to produce high calibre science graduates with sought after skills in critical thinking, analysis, interpretation and communication. Technology has continued to advance at a similar pace providing those responsible for managing crime with a need and opportunity to identify and predict new and future applications of science and technology; not just in reducing and detecting crime but also in predicting how technology will be used by criminals in the future. There is therefore a need for forensic science users, providers and educators to identify the knowledge and skills required by forensic scientists and crime investigators of the future to ensure that technology continues to be used and applied to its full advantage. This provides universities an opportunity to contribute to the development of both the practice and practitioners of forensic science. This paper outlines the current issues facing universities in relation to forensic science and identifies their future role in providing high quality relevant courses for future forensic practitioners; developing current forensic practitioners through their participation in applied research, short courses, conferences and qualifications linked to professional practice; and supporting and developing the practice of forensic and crime scene science, through the identification, engagement and dissemination of pure and applied research.