The use of ethyl cellulose film lifts to collect particle traces from exposed adhesive on the edges of duct tape.

Environmentally acquired particles (EAP), trapped along the edges of duct tape in the exposed adhesive, are a possible source of information regarding prior exposures of the tape and a possible means to associate duct tape rolls to segments of duct tape that are collected as traces during the investigation of criminal activity. The recovery and separation of EAP is complicated by (1) the need to separate the particles from the adhesive, and (2) the presence of adhesive filler and pigment particles that are part of adhesive formulations. Approaches such as cutting the tape edge, followed by solvent extraction, or swabbing of the duct tape edges using solvents, result in thousands of adhesive filler/pigment particles, overwhelming much smaller numbers of EAP. A recovery method has been developed employing a 10% solution of ethylcellulose (EC) in ethanol. Duct tape segments are pressed onto a glass plate and a bead of the viscous EC solution is pipetted along the edge. After drying, the EC forms a robust film that is peeled away from the tape edge, lifting the EAP along with only very small amounts of adhesive. The film lift (containing EC, duct tape adhesive and EAP) can be examined directly by steromicroscopy and particles of interest can be removed by softening the film using locally applied ethanol. Particles can be examined in situ by transmitted light microscopy using glycerol as a mounting medium to match the EC film. Batch recovery of particles from the film can be achieved by dissolution of the film lift in xylene and washing to remove adhesive residues. Xylene is then removed by washing with ethanol, leaving an ethanol suspension of EAP along with the duct tape filler/pigment particles. Larger particles can be separated by sieving and smaller particles can be recovered by filtration. This method was found to efficiently collect EAP found trapped along the edges of duct tape in the exposed adhesive, as well as for the preparation of these particles for microscopical and instrumental analysis. Limitations, not fully evaluated, include the loss or alteration of some particle types by dissolution, agitation and filtration steps. Further development of this method is expected to provide a means to recover trace particles from the edges of other types of tape and from related adhesive products such as stamps and labels.

Identification of factors affecting SEM/EDS analysis for discrimination and classification among common items of evidence using particle combination profiles.

This article presents key factors affecting the analysis of particle profiles as used for discrimination and classification among items commonly collected at crime scenes. Identification of these factors is a necessary step to enable systematic improvement, optimization, and transition to practice. Prior research, employing reasonable initial choices of analytical and statistical parameters, has (1) demonstrated the presence of highly discriminating sets of very small particles (VSP) on the surfaces of items commonly collected at crime scenes, (2) developed statistically rigorous measurements of correspondence between VSP profiles, and (3) produced objective measures for the resulting probative value. In the present work the analytical and statistical parameters were examined more critically, identifying key factors affecting method performance. Experiments were conducted using scanning electron microscopy (SEM) with energy dispersive x-ray elemental analysis (EDS) to characterize the elemental composition of thousands of individual particles within each specimen. The experiments studied: Reproducibility of VSP analyses at given parameters Effects of the SEM/EDS parameters used for the detection of each particle Effects of SEM/EDS x-ray analysis parameters used for elemental analysis of each particle Effects of the number and choice of elements used in the elemental analysis Effects of particle size on the strength of correspondence between particle sets Effects of data filtration parameters on the strength of correspondence between particle sets The experiments confirmed the presence of abundant, highly discriminating VSP on items commonly collected at crime scenes. The numbers of particles available for analysis was not a limiting factor: many more particles (usually greater than 50 times more) were present than were used for the analysis. A very high level of reproducibility was observed. Many of the parameters tested had no measurable effect on particle combination analysis performance and others had minor or interactive effects. Four factors were identified as having significant impact on the strength of correspondence between particle profiles, three factors were identified as having a significant impact on the numbers of particles detected and nine factors were identified as having a significant impact on analytical time and costs. The approach in its current state of development offers crime laboratories an additional capability suitable for high priority cases. The identification of key factors affecting performance of the VSP analytical protocol allows existing methods to be further developed and systematically improved to facilitate transition to routine practice.

Utility of Non-Identifiable Fingermarks.

Fingermarks that have insufficient characteristics for identification often have discernible characteristics that can form the basis for lesser - yet still useful - degrees of correspondence and probability of occurrence within a population. Currently, those fingermarks that experts judge to be insufficient for identification are not used as associative evidence. However, recent research has shown large numbers of cases where non-identifiable fingermarks (NIFMs) occur that have high potential associative value. The present work focuses on the resulting questions of, "How useful could associations from NIFMs be in actual practice?" and, "What developments or improvements are needed to take advantage of this very promising potential?" As a first step toward answering these questions, the results of recent research findings on occurrence and associative value of NIFMs were presented to a broad audience of criminal justice participants and stakeholders in the United States, including police investigators, prosecutors, judges, defense attorneys, forensic scientists, and members of the academic and research communities. There were a series of extensive, open ended discussions aimed at obtaining individual reactions, including views on the potential contribution in different circumstances and at different stages in the criminal justice process, issues that would affect this contribution, approaches to development, and areas of concern. This produced several important insights. As a class of evidence, NIFM associations were found to be material, clearly distinct from conventional fingermark evidence, and exceptional among less definitive classes of evidence. A wide range of potential contributions were revealed at different levels in the criminal justice process. Some areas of application are suitable for immediate use. Other areas require further development or research in the methodologies, and still others must await developments in forensic science as a whole. There are important implications for researchers, practitioners, evidence collection strategies and evidence retention policies.

Occurrence and associative value of non-identifiable fingermarks.

Fingermarks that have insufficient characteristics for identification often have discernible characteristics that could form the basis for lesser degrees of correspondence or probability of occurrence within a population. Currently, those latent prints that experts judge to be insufficient for identification are not used as associative evidence. How often do such prints occur and what is their potential value for association? The answers are important. We could be routinely setting aside a very important source of associative evidence, with high potential impact, in many cases; or such prints might be of very low utility, adding very little, or only very rarely contributing to cases in a meaningful way. The first step is to better understand the occurrence and range of associative value of these fingermarks. The project goal was to explore and test a theory that in large numbers of cases fingermarks of no value for identification purposes occur and are readily available, though not used, and yet have associative value that could provide useful information. Latent fingermarks were collected from nine state and local jurisdictions. Fingermarks included were those (1) collected in the course of investigations using existing jurisdictional procedures, (2) originally assessed by the laboratory as of no value for identification (NVID), (3) re-assessed by expert review as NVID, but with least three clear and reliable minutiae in relationship to one another, and (4) determined to show at least three auto-encoded minutiae. An expected associative value (ESLR) for each mark was measured, without reference to a putative source, based on modeling within-variability and between-variability of AFIS scores. This method incorporated (1) latest generation feature extraction, (2) a (minutiae-only) matcher, (3) a validated distortion model, and (4) NIST SD27 database calibration. Observed associative value distributions were determined for violent crimes, property crimes, and for existing objective measurements of latent print quality. 750 Non Identifiable Fingermarks (NIFMs) showed values of Log10 ESLR ranging from 1.05-10.88, with a mean value of 5.56 (s.d. 2.29), corresponding to an ESLR of approximately 380,000. It is clear that there are large numbers of cases where NIFMs occur that have high potential associative value as indicated by the ESLR. These NIFMs are readily available, but not used, yet have associative value that could provide useful information. These findings lead to the follow-on questions, "How useful would NIFM evidence be in actual practice?" and, "What developments or improvements are needed to maximize this contribution?"

Differential analysis of very small particles (VSP) from the contact surfaces and recessed areas of footwear.

Prior work has shown that the contact surfaces of footwear rapidly lose very small particles (VSP) when walking on dry soil. Other research, with more general sampling from shoe soles, has shown that particles can persist much longer. Given rapid losses from contact surfaces, we hypothesize that non-contact, recessed areas of footwear retain particles from prior exposures. Here we conduct differential analysis of VSP recovered separately from contact and recessed surfaces, following a controlled series of environmental exposures. Work boots and tennis shoes were exposed by walking distances of 250 m, sequentially, in three environmental sites. VSP were harvested separately from contact and recessed surfaces using a moist swabbing procedure. VSP were analyzed by microscopy and the proportions attributable to each site were determined using a newly developed statistical model. The principal findings are (1) contact surfaces of footwear are dominated by VSP attributable to the most recent site of exposure, (2) recessed surfaces of footwear retain VSP from prior exposures, (3) sole type appears to be a source of major differences in the amount of VSP from prior exposures remaining in recessed areas, and (4) when VSP attributable to prior exposures are found, there is no clear trend for dominance between earlier exposures. The significance of these findings is considerable. In cases where the last site visited is of interest, VSP from contact surfaces of footwear will give a nearly pure sample of that site. In cases where prior sites visited are of interest, the VSP from the contact surfaces can be used as a background signal, providing a means for differential analysis of VSP mixtures found in the recessed areas of the sole. The strong influence of shoe sole type on the retention of VSP from prior exposures indicates that efforts to explore the rates of VSP loss from recessed areas will need to take characteristics of the sole type into account. The absence of a clear trend for dominance between earlier exposures suggests that once traces are lodged within the recessed areas of footwear soles they can be retained for long periods of time. These findings support prior research on the retention of particles on footwear that shows periods of long retention following rapid initial losses of trace materials. The differential analysis of VSP is a significant contribution to the methods available for the deconvolution of particle mixtures into fractions that are characteristic of their contributing sources.

Rates of loss and replacement of very small particles (VSP) on the contact surfaces of footwear during successive exposures.

It has previously been shown that a walk of 250 m (approximately 175 steps/shoe) in a new environment is sufficient to remove and replace particles present on the contact surfaces of footwear. However, it is unknown how quickly this replacement occurs. This paper describes experiments measuring how quickly (in terms of steps) this loss and replacement of VSP occurs. Three environmental exposure sites were chosen to have different, characteristic particle types (soil minerals). Footwear of two types (work boots and tennis shoes) were tested, accumulating particles by walking 250 m in one site, followed by walking a designated number of steps (per shoe) in a second site. Very small particles (VSP) were harvested from contact surfaces of the footwear (those surfaces in direct contact with the ground when walking) using a moist swabbing procedure. The resulting numbers and types of VSP were determined using forensic microscopy and the proportions of VSP attributable to the first and second site were determined by particle combination analysis using a latent Dirichlet allocation model. The principal findings from this study are (1) that the contact surfaces of footwear are dominated by VSP attributable to the most recent site of exposure, (2) that walking in a new location rapidly removes and replaces VSP from the contact surfaces of footwear, (3) major replacement occurs in 5 to 10 steps and nearly complete replacement occurs by 25 steps, (4) the character of the loading site may influence the initial rate of loss and replacement of VSP (during the first five steps), and (5) overall, the loss and replacement of VSP on footwear in these experiments can be reasonably described by the relationship 1/(Steps + 2.68). The significance of these findings is considerable. In cases where the last site visited is of interest, VSP from contact surfaces of footwear will give a nearly pure sample of that site. In cases where prior sites visited are of interest, the VSP from the contact surfaces can be used as a background signal, providing a necessary beginning for efforts to resolve mixtures of VSP arising from different exposures. The usefulness of VSP on footwear evidence depends on developing this ability so that a reliable, relevant evidentiary "signal" can be separated from background noise (or signals from other exposures).

Discrimination and classification among common items of evidence using particle combination profiles.

This project used established analytical tools and statistical methods to determine the evidential value of very small particle (VSP) profiles found on handguns, cell phones, drug packaging, and ski masks. Sampling protocols were designed, tested and used to sample VSP from evidence items from a single county-level crime laboratory: 30 handguns, 31 cell phones, 36 drug packaging specimens and 32 ski masks. Specimens were prepared for analysis employing established protocols for semi-automated scanning electron microscopy with elemental characterization by energy dispersive x-ray analysis (SEM/EDS). Statistical methods of particle combination analysis were applied to (1) remove particle "noise" from the datasets, (2) define a set of highly discriminating target particle types, (3) measure the strength of correspondence between profiles, and (4) measure the potential of VSP as an evidence type under defined experimental conditions. Most (84%) of the VSP specimens recovered from common evidence items showed sufficient variety and complexity in their VSP profiles to allow meaningful classification among closed sets of approximately 30 specimens. Correct associations were achieved for 93.5% of test specimens (drug packaging: 97.2%; cell phones: 92.6%; handguns: 92.9%; ski masks 88.2%). Test specimens with VSP numbers greater than 125 showed predominantly correct classifications. These findings establish (1) that VSP are present on the surfaces common items of physical evidence, (2) that the VSP can be efficiently recovered, prepared and analyzed by computer-assisted SEM/EDS analysis, (3) that the variety of particles is sufficient for the definition of classifiers based on reference sources, and (4) that the classifiers perform very well for these particle sets, showing that VSP recovery, analytical methods and computational methods are working effectively. The use of adhering VSP to establish quantitative associations among items of physical evidence is a new approach, exploiting a form of trace evidence that is typically ignored. It is highly significant for its potential to expand the number of cases to which trace evidence can meaningfully contribute and for its ability to include a quantitative statistical approach to data interpretation.

Loss and replacement of small particles on the contact surfaces of footwear during successive exposures.

On the contact surfaces of footwear loosely, moderately and strongly held particle fractions were separated and analyzed in an effort to detect different particle signals. Three environmental exposure sites were chosen to have different, characteristic particle types (soil minerals). Shoes of two types (work boots and tennis shoes) were tested, accumulating particles by walking 250m in each environment. Some shoes were exposed to only one environment; others were exposed to all three, in one of six different sequences. Sampling methods were developed to separate particles from the contact surface of the shoe based on how tightly they were held to the sole. Loosely held particles were removed by walking on paper, moderately held particles were removed by electrostatic lifting, and the most tightly held particles were removed by moist swabbing. The resulting numbers and types of particles were determined using forensic microscopy. Particle profiles from the different fractions were compared to test the ability to objectively distinguish the order of exposure to the three environments. Without exception, the samples resulting from differential sampling are dominated by the third site in the sequential footwear exposures. No noticeable differences are seen among the differential samplings of the loosely, moderately and strongly held particles: the same overwhelming presence of the third site is seen. It is clear from these results (1) that the third (final) exposure results in the nearly complete removal of any particles from prior exposures, and (2) that under the experimental conditions loosely, moderately and strongly held particles are affected similarly, without any detectable enrichment of the earlier exposures among the more tightly held particles. These findings have significant implications for casework, demonstrating that particles on the contact surfaces of footwear are rapidly lost and replaced.

Utilization of environmentally acquired very small particles as a means of association.

Very small particles (VSP) are ubiquitous in our environment and are virtually ignored by forensic science. These particles range in size from an order of magnitude smaller than conventional trace evidence, down to the molecular level. Combinations of VSP provide an extraordinary, largely untapped resource for forensic associations and source attribution. This paper describes an initial effort to exploit VSP for one specific application. An approach was developed and tested for the SEM/EDS analysis of VSP recovered from the surfaces of carpet fibers - one of the most common types of trace evidence examined in crime laboratories. Our goal was to exploit existing computer-assisted SEM/EDS methods to test whether VSP profiles could be useful to associate shed fibers with a source carpet. Particles were harvested by washing and filtration onto polycarbonate filters. An SEM/EDS analysis protocol currently employed for environmental particle analyses was used, resulting in individual particle characterization based on fitting to reference spectra of 28 elements. Target Particle Types were defined based on the most abundant elemental profiles and used to bin the results for each specimen, resulting in a Target Particle Type profile. Within-carpet variability was assessed using Target Particle Type profiles from three different areas on each of nine carpets. Area profiles, defined from sets of ten fibers, were compared to profiles from individual fibers. Between-item variation was explored using a survey of an additional 12 carpets. Hundreds to thousands of VSP were found to routinely occur on individual carpet fibers. Their quantity and character was sufficient to associate fibers with their area of origin. Within-carpet variations showed roughly even distributions for most TPTs and between-carpet variations showed wide ranges in types and quantities of VSP. Environmentally acquired VSP showed clear potential to provide quantitative means to link carpet fibers with their area of origin. This finding is noteworthy, since such particles are acquired post-manufacture and are independent of characteristics determined by manufacture. More generally, VSP are ubiquitous, present on or in virtually any item, and there is the potential for linkages among items of any type based on adhering VSP. By way of example, the present work provides impetus for a fundamental change in the way that forensic trace evidence is conceptualized. Further fundamental research is indicated to better understand the underlying variability, usefulness and limitations of this approach.

Illustration and analysis of a coordinated approach to an effective forensic trace evidence capability.

An effective trace evidence capability is defined as one that exploits all useful particle types, chooses appropriate technologies to do so, and directly integrates the findings with case-specific problems. Limitations of current approaches inhibit the attainment of an effective capability and it has been strongly argued that a new approach to trace evidence analysis is essential. A hypothetical case example is presented to illustrate and analyze how forensic particle analysis can be used as a powerful practical tool in forensic investigations. The specifics in this example, including the casework investigation, laboratory analyses, and close professional interactions, provide focal points for subsequent analysis of how this outcome can be achieved. This leads to the specification of five key elements that are deemed necessary and sufficient for effective forensic particle analysis: (1) a dynamic forensic analytical approach, (2) concise and efficient protocols addressing particle combinations, (3) multidisciplinary capabilities of analysis and interpretation, (4) readily accessible external specialist resources, and (5) information integration and communication. A coordinating role, absent in current approaches to trace evidence analysis, is essential to achieving these elements. However, the level of expertise required for the coordinating role is readily attainable. Some additional laboratory protocols are also essential. However, none of these has greater staffing requirements than those routinely met by existing forensic trace evidence practitioners. The major challenges that remain are organizational acceptance, planning and implementation.

Exploitation of very small particles to enhance the probative value of carpet fibers.

Environmentally acquired very small particles (VSP), present on the surfaces of carpet fibers, have shown potential for the association of fibers with their carpet source. To unlock this potential, research is required addressing a number of areas, including the application of methods under realistic casework conditions and the utilization of computational methods for the refinement and testing of the approach. In this work field collections of carpet fibers were conducted by crime scene practitioners under realistic casework conditions. VSP were isolated using previously developed methods, and analyses were conducted using SEM/EDS analytical protocols in an operational crime laboratory setting. Computational methods were designed, allowing sets of hundreds to thousands of VSP to be characterized. Classifiers were designed to associate and discriminate among specimens. These classifiers were applied to the VSP data for specimens collected by crime scene practitioners, as well as to a previously collected research dataset. Quantitative measures of correspondence and probative value were designed based on the classification measures and successfully applied to both sets of VSP data. Particle sets larger than 500 showed strong promise for quantitative associations with their sources. The use of larger numbers of target particle types (TPTs) showed strong promise to improve the performance of classification and association. Overall, the usefulness of VSP to provide objective, quantitative associations has been established. Because VSP are acquired post-manufacture, these methods can address fundamental limitations to probative value that arise when class characteristics, determined by manufacture, are shared among mass produced commodities. These findings are of broad significance for the future of trace evidence analysis. The results of this research are likely extendable, with minor modifications, to other trace evidence types (such as glass, tape and human hair), and are expected to contribute significantly for those types of trace evidence that have long been considered of low evidential value (such as undyed cotton and animal hairs). Furthermore, entirely new approaches to trace evidence are enabled by exploiting VSP profiles, such as comparing different types of trace evidence with one another and comparing VSP defined by crime scene or suspect environments to those on virtually any item of physical evidence.

Critical review of forensic trace evidence analysis and the need for a new approach.

The historical development, contributions and limitations of the two traditional approaches to trace evidence analysis are reviewed. The first approach was as generalist practitioner, looking broadly at an assemblage of many different particle types. The second was that of specialist practitioner, with attention focused on one specific particle type. Four factors have significantly impacted the effectiveness of these approaches: (1) increasing technological capabilities, (2) increasing complexity in the character of manufactured materials, (3) changes in forensic laboratory management, and (4) changing scientific and legal expectations. The effectiveness of each approach is assessed within the context of these changes. More recently, new technologies have been applied to some trace evidence problems, intended to address one or more limitations. This has led to a third approach founded on discrete, highly technical methods addressing specific analytical problems. After evaluating the contributions and limitations of this third approach, we consider the different ways that technologies could be developed to address unmet needs in forensic trace evidence analysis. The route toward effective use of new technologies is contrasted with how forensic science laboratories are currently choosing and employing them. The conclusion is that although new technologies are contributing, we are not on a path that will result in their most effective and appropriate use. A new approach is required. Based on an analysis of the contributions of each of the three exisiting approaches, seven characteristics of an effective trace evidence analysis capability were determined: (1) particle traces should be a major problem-solving tool, (2) there should be readily available, straightforward methods to enable their use, (3) all available and potentially useful particle types should be considered, (4) decisions to use them should be made in the context of each case, guided by what they can contribute to the case and how efficiently they can do so, (5) analyses should be conducted using appropriate technologies, (6) findings should be timely and directly integrated with case-specific problems, and (7) new technologies should be used to improve the overall effectiveness of the capability. Clearly new technologies have the potential to revolutionize forensic trace evidence, but just as clearly some of the traditional capabilities have been rendered ineffective, or lost entirely, by the way we have come to approach the problem. Having critically defined the current limitations of and the desired outcomes, the next focus should be consideration of alternative approaches that might achieve such a result.

A selection of some of Dr. McCrone's high and low profile cases in the forensic analysis of art.

Throughout Dr. McCrone's active professional career of over 60 years, he worked on many cases involving the forensic analysis of art. This is an overview of a small portion of these cases. Included (exposed as fakes) are the Shroud of Turin, the Vinland Map, Mayan pottery illustrations and Larionov pastels. Also included, with strong support for authentication, are three paintings attributed to Manet, Giorgione, and Leonardo da Vinci.