Validation of likelihood ratio methods for forensic evidence evaluation handling multimodal score distributions

This paper is a postprint of a paper submitted to and accepted for publication in IET Biometrics and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at IET Digital LibraryThis article presents a method for computing Likelihood Ratios (LR) from multimodal score distributions produced by an Automated Fingerprint Identification System (AFIS) feature extraction and comparison algorithm. The AFIS algorithm used to compare fingermarks and fingerprints was primarily developed for forensic investigation rather than for forensic evaluation. The computation of the scores is speed-optimized and performed on three different stages, each of which outputs discriminating scores of different magnitudes together forming a multimodal score distribution. It is worthy mentioning that each fingermark to fingerprint comparison performed by the AFIS algorithm results in one single similarity score (e.g. one score per comparison). The multimodal nature of the similarity scores can be typical for other biometric systems and the method proposed in this work can be applied in similar cases, where the multimodal nature in similarity scores is observed. In this work we address some of the problems related to modelling such distributions and propose solutions to issues like data sparsity, dataset shift and over-fitting. The issues mentioned affect the methods traditionally used in the situation when a multimodal nature in the similarity scores is observed (a Kernel Density Functions (KDF) was used to illustrate these issues in our case). Furthermore, the method proposed produces interpretable results in the situations when the similarity scores are sparse and traditional approaches lead to erroneous LRs of huge magnitudesThe research was conducted in scope of the BBfor2 – Marie Curie Initial Training Network (FP7-PEOPLE-ITN-2008 under the Grant Agreement 238803) at the Netherlands Forensic Institute in cooperation with the ATVS Biometric Recognition Group at the Universidad Autonoma de Madrid and the National Police Services Agency of the Netherland

Measuring coherence of computer-assisted likelihood ratio methods

This is the author’s version of a work that was accepted for publication in Forensic Science International. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Forensic Science International, 249 (2015): 123 – 132 DOI:10.1016/j.forsciint.2015.01.033Measuring the performance of forensic evaluation methods that compute likelihood ratios (LRs) is relevant for both the development and the validation of such methods. A framework of performance characteristics categorized as primary and secondary is introduced in this study to help achieve such development and validation. Ground-truth labelled fingerprint data is used to assess the performance of an example likelihood ratio method in terms of those performance characteristics. Discrimination, calibration, and especially the coherence of this LR method are assessed as a function of the quantity and quality of the trace fingerprint data. Assessment of the coherence revealed a weakness of the comparison algorithm in the computer-assisted likelihood ratio method used.This research was conducted in the scope of the BBfor2 – European Commission Marie Curie Initial Training Network (FP7-PEOPLE-ITN-2008 under Grant Agreement 238803) at the Netherlands Forensic Institute, and in collaboration with the ATVS Biometric Recognition Group at the Universidad Autonoma de Madrid and the National Police Services Agency of the Netherlands

Investigation into the effect of fingermark detection chemicals on the analysis and comparison of pressure-sensitive tapes.

Pressure sensitive tapes such as duct tape are a common trace type sent for forensic analysis. The limited variation of tape backings and adhesives can provide valuable linkage evidence between a scene, a victim or a person of interest. Fingermarks are also often found on tapes and prioritised over tape analyses. This project aimed to investigate the effects of fingermark enhancement chemicals, namely Wet Powder™, cyanoacrylate and cyanoacrylate stained with rhodamine 6G, on various tapes and their comparison with untreated tapes. The changes in physical and optical features were observed using a Video Spectral Comparator (VSC) and microscopy. Chemical changes were analysed by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR). Most physical and optical properties were not heavily affected by the treatments. An increase in fluorescence was observed with specimens stained with rhodamine 6G as might be expected. Significant chemical changes were observed in the FTIR spectra produced from cyanoacrylate fuming. Polyethylene backings and rubber adhesives were heavily affected while polypropylene backings were moderately affected. Cellulose backings, polyester and polyacrylate adhesives were not significantly affected. Wet Powder™ treatment proved useful for enhancing fingermarks on most adhesives while leaving behind little chemical residue that might interfere in a forensic comparison

Information-theoretical assessment of the performance of likelihood ratio computation methods

This is the accepted version of the following article: Ramos, D., Gonzalez-Rodriguez, J., Zadora, G. and Aitken, C. (2013), Information-Theoretical Assessment of the Performance of Likelihood Ratio Computation Methods. Journal of Forensic Sciences, 58: 1503–1518. doi: 10.1111/1556-4029.12233, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/1556-4029.12233/Performance of likelihood ratio (LR) methods for evidence evaluation has been represented in the past using, for example, Tippett plots. We propose empirical cross-entropy (ECE) plots as a metric of accuracy based on the statistical theory of proper scoring rules, interpretable as information given by the evidence according to information theory, which quantify calibration of LR values. We present results with a case example using a glass database from real casework, comparing performance with both Tippett and ECE plots. We conclude that ECE plots allow clearer comparisons of LR methods than previous metrics, allowing a theoretical criterion to determine whether a given method should be used for evidence evaluation or not, which is an improvement over Tippett plots. A set of recommendations for the use of the proposed methodology by practitioners is also given.Supported by the Spanish Ministry of Science and Innovation under project TEC2009-14719-C02-01 and co-funded by the Universidad Autonoma de Madrid and the Comunidad Autonoma de Madrid under project CCG10-UAM/TIC-5792

Evaluating the efficiency and sensitivity of one-step cyanoacrylate fuming methods in the detection and visualisation of latent fingerprints on the adhesive side of tape

The evidential value of adhesive tape recovered from a crime scene plays a critical role in the criminal investigation as it could potentially contain things such as fibres, hair, DNA evidence, or fingerprints. Adhesive tape is a ubiquitous material that can be used in crimes that involve kidnapping and murder, as well as used to house cables in acts of terrorism. With regards to the adhesive side of tape, the sticky nature of this surface not only increases the likelihood of latent fingerprint deposits but has routinely proved to be a problematic substrate to work with. As latent fingerprints are generally invisible to the eye, enhancement methods are required to conduct adequate analysis on the fingerprint details. Despite several methods of fingerprint enhancement available, common issues including high background staining and low selectivity of fingerprint deposits create a difficult problem for forensic investigators to solve. Studies have shown that these issues can be overcome by utilising aqueous solutions of fingerprint powders, as well as traditional dye methods like gentian violet. Fluorescent dyes have also been explored and shown to be very effective when used on darker-coloured adhesive tapes. With regards to aged latent fingerprints, sticky-side powder and phase transfer catalysts have proven to be viable methods of detection and development. Traditional cyanoacrylate fuming was observed to be the best method of development in all reviewed cases, but the requirement of subsequent dye staining poses potential health issues to the user and the environment. One-step cyanoacrylate fuming has been proposed as a method incorporating the staining step into the cyanoacrylate fuming step, thus completing both steps simultaneously. As one-step cyanoacrylate fuming is a relatively new method of development, its potential application to the development of latent fingerprints on the adhesive side of tape has not been explored to its full extent and should be researched more extensively

BioTwist - overcoming severe distortions in ridge-based biometrics for successful identication

Biometrics rely on a physical trait's permanence and stability over time, as well as its individuality, robustness and ease to be captured. Challenges arise when working with newborns or infants because of the tininess and fragility of an infant's features, their uncooperative nature and their rapid growth. The last of these is particularly relevant when one tries to verify an infant's identity based on captures of a biometric taken at an earlier age. Finding a physical trait that is feasible for infants is often referred to as the infant biometric problem. This thesis explores the quality aspect of adult fingermarks and the correlation between image quality and the mark’s usefulness for an ongoing forensic investigation, and researches various aspects of the “ballprint” as an infant biometric. The ballprint, the friction ridge skin area of the foot pad under the big toe, exhibits similar properties to fingerprint but the ball possesses larger physical structures and a greater number of features. We collected a longitudinal ballprint database from 54 infants within 3 days of birth, at two months old, at 6 months and at 2 years. It has been observed that the skin of a newborn's foot dries and cracks so the ridge lines are often not visible to the naked eye and an adult fingerprint scanner cannot capture them. This thesis presents the physiological discovery that the ballprint grows isotropically during infancy and can be well approximated by a linear function of the infant's age. Fingerprint technology developed for adult fingerprints can match ballprints if they are adjusted by a physical feature (the inter-ridge spacing) to be of a similar size to adult fingerprints. The growth in ballprint inter-ridge spacing mirrors infant growth in terms of length/height. When growth is compensated for by isotropic rescaling, impressive verification scores are achieved even for captures taken 22 months apart. The scores improve even further when low-quality prints are rejected; the removal of the bottom third improves the Equal Error Rate from 1-2% to 0%. In conclusion, this thesis demonstrates that the ballprint is a feasible solution to the infant biometric problem

Forging a Stable Relationship?: Bridging the Law and Forensic Science Divide in the Academy

The marriage of law and science has most often been represented as discordant. While the law/science divide meme is hardly novel, concerns over the potentially deleterious coupling within the criminal justice system may have reached fever pitch. There is a growing chorus of disapproval addressed to ‘forensic science’, accompanied by the denigration of legal professionals for being unable or unwilling to forge a symbiotic relationship with forensic scientists. The 2009 National Academy of Sciences Report on forensic science heralds the latest call for greater collaboration between ‘law’ and ‘science’, particularly in Higher Education Institutions (HEIs) yet little reaction has been apparent amid law and science faculties. To investigate the potential for interdisciplinary cooperation, the authors received funding for a project: ‘Lowering the Drawbridges: Forensic and Legal Education in the 21st Century’, hoping to stimulate both law and forensic science educators to seek mutually beneficial solutions to common educational problems and build vital connections in the academy. A workshop held in the UK, attended by academics and practitioners from scientific, policing, and legal backgrounds marked the commencement of the project. This paper outlines some of the workshop conclusions to elucidate areas of dissent and consensus, and where further dialogue is required, but aims to strike a note of optimism that the ‘cultural divide’ should not be taken to be so wide as to be beyond the legal and forensic science academy to bridge. The authors seek to demonstrate that legal and forensic science educators can work cooperatively to respond to critics and forge new paths in learning and teaching, creating an opportunity to take stock and enrich our discipline as well as answer critics. As Latham (2010:34) exhorts, we are not interested in turning lawyers into scientists and vice versa, but building a foundation upon which they can build during their professional lives: “Instead of melding the two cultures, we need to establish conditions of cooperation, mutual respect, and mutual reliance between them.” Law and forensic science educators should, and can assist with the building of a mutual understanding between forensic scientists and legal professionals, a significant step on the road to answering calls for the professions to minimise some of the risks associated with the use of forensic science in the criminal process. REFERENCES Latham, S.R. 2010, ‘Law between the cultures: C.P.Snow’s The Two Cultures and the problem of scientific illiteracy in law’ 32 Technology in Society, 31-34. KEYWORDS forensic science education legal education law/science divid

An investigation of fingermark submission decision making

This thesis investigates the submission of fingermark evidence from the fingerprint laboratory (where the enhancement of crime scene fingermarks occurs) to the fingerprint bureau (where examiners compare crime scene and suspect fingermarks) within UK forensic science. Initial research presented in this thesis identifies a discrepancy between laboratory practitioner mark submission decision making and the usability decisions made by fingerprint examiners, in the case of ambiguous fingermarks, leading to the potential for a loss of evidence that could be used to identify a suspect. Further empirical research explores the components of this decision process through consideration of decision success, cues, thresholds, and factors that influence the decision process. Qualitative research explores the rationale behind the mark submission decisions of practitioners, identifying a common reliance on a numerical value of characteristics present as a threshold for submission. The reliability of the use of a minutiae count as a method for increasing the objectivity of the submission is further investigated and variation between the minutiae cue detection of practitioners and examiners is identified. A contrast effect is found to occur in relation to practitioners making submission decisions concerning fingermarks in situ on exhibits that contain background marks, and this effect is discussed in relation to the differences in practitioner and examiner quality determination procedure. The findings of these empirical studies are presented and explained in terms of psychological theories of judgement and decision making, as well as in terms of their procedural and practical implications for fingerprint evidence recovery, and their wider implication within the holistic forensic process and criminal justice system