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Rapid advances and decreased production costs in 3D printing (3DP) have resulted in its accelerated implementation in criminal activities. Fused Deposition Modeling (FDM (3DP and Polylactic Acid (PLA) filament were chosen for the current research because they are widely used in commodity 3DP, particularly in documented criminal activities. This study shows how specific features of 3DP along with classical toolmark comparison techniques using Stereo-Microscopy and Comparison Microscopy can be used to link between two 3DP objects as well as between a printed object and a suspected 3D printer. Links are determined based on random fine marks found on the 3DP's heated stage (bed) that are replicated to the base face of the printed object. Melted filament that extrudes from the nozzle of the FDM 3DP constructs the base face of the printed object. This melted filament functions as a "casting material" after it cools down and solidifies, enabling replication of the fine marks. The observed resolution of these marks is as high as the resolution of casting material dedicated for toolmark replications. Overall, this study demonstrates a novel forensic method based on toolmark comparison for linking between a 3D printer and its printed objects.

The current methodology for indented writing detection involves electrostatic detection apparatus (ESDA) processing and oblique light. While commonly used in forensics analysis, ESDA has several drawbacks, including its unsuitability for documents of certain shapes and densities, the damage it occasionally causes to evidence, its need for prior humidification in order to process documents, and the ozone it creates. In this study we evaluated optical profilometry as an alternative to ESDA. We tested several optical profilometer brands and showed their capacity for detecting very slight indentations, even to the magnitude of 8µm. We also obtained the clear resolution of a 3D image of this writing.

Footwear comparison is used to link between a suspect's shoe and a shoeprint found at a crime scene. Forensic examiners compare the two items, and the conclusion reached is based on class characteristics and randomly acquired characteristics (RACs), such as scratches or holes. An important question concerns the distribution of the location of RACs on shoe soles, which can serve as a benchmark for comparison. This study examines the probability of observing RACs in different areas of a shoe sole using a database of approximately 13,000 RACs observed on 386 outsoles. The analysis is somewhat complicated as the shoes are differentiated by shape and contact surface, and the RACs' locations are subject to measurement errors. A method that takes into account these challenges is presented. All impressions are normalized to a standardized axis to allow for inter-comparison of RACs on outsoles of different sizes and contact areas, and RACs are localized to one of 14 subareas of the shoe sole. Expected frequencies in each region are assumed to be Poisson distributed with rate parameters that depend on the subarea and the contact surface. Three different estimation approaches are studied: a naive crude approach, a shoe-specific random effects model, and an estimate that is based on conditional maximum likelihood. It is shown that the rate is not uniform across the shoe sole and that RACs are approximately twice as likely to appear at certain locations, corresponding to the foot's morphology. The results can guide investigators in determining a shoeprint's evidential value.

In recent years, there is a growing demand to fortify the scientific basis of forensic methodology. During 2016, the President's Council of Advisors on Science and Technology (PCAST) published a report that states there are no appropriate empirical studies that support the foundational validity of footwear analysis to associate shoeprints with particular shoes based on specific identifying marks, which is a basic scientific demand from the field. Furthermore, meaningful databases that can support such studies do not exist. Without such databases, statistical presentation of the comparison results cannot be fulfilled either. In this study, a database of over 13,000 randomly acquired characteristics (RACs) such as scratches, nicks, tears, and holes, as they appear on shoe sole test impressions, from nearly 400 shoe soles was collected semi-automatically. The location, orientation, and the contour of each RAC were determined for all the RACs on each test impression. The statistical algorithm Statistic Evaluation of Shoeprint Accidentals (SESA) was developed to calculate a score for finding another feature similar to a particular scanned and digitized RAC in the same shape, location, and orientation as the examined one. A correlation was found between the results of SESA and the results of real casework, strengthening our belief in the ability of SESA to assist the expert in reaching a conclusion while performing casework. The score received at the end of the process serves the expert as a guiding number, allowing more objective and accurate results and conclusions.

Randomly acquired characteristics (RACs), also known as accidental marks, are random markings on a shoe sole, such as scratches or holes, that are used by forensic experts to compare a suspect's shoe with a print found at the crime scene. This article investigates the relationships among three features of a RAC: its location, shape type and orientation. If these features, as well as the RACs, are independent of each other, a simple probabilistic calculation could be used to evaluate the rarity of a RAC and hence the evidential value of the shoe and print comparison, whereas a correlation among the features would complicate the analysis. Using a data set of about 380 shoes, it is found that RACs and their features are not independent, and moreover, are not independent of the shoe sole pattern. It is argued that some of the dependencies found are caused by the elements of the sole. The results have important implications for the way forensic experts should evaluate the degree of rarity of a combination of RACs.

Shoeprints left at crime scenes are seldom perfect. Many prints are distorted or contaminated by various materials. Noisy background often contributes to vagueness on the shoeprints as well. Test impressions made from the suspect's shoes in the laboratory are considered a genuine replication of the shoe-sole. This naive attitude is far from being correct. Consecutive test impressions made in the laboratory under strict similar conditions revealed differences among the exemplars of the same sole. Some of them are minor, but some are major, and can mislead the less experienced practitioners during the comparison process. This article focuses on the inherent within source variability between controlled shoeprints made from the same shoe, as it appears on the RACs. To describe and analyze this variability, repeated test impressions were prepared, and datasets were created. Several RACs were marked on each test impression, using an expert assisting software tool (developed in the authors' lab). The variance in repeated test impressions is demonstrated and possible sources are discussed. This variance should be considered when trying to establish the degree of matching between individual characteristics.

Dusty shoeprints can be found on various substrates and should be dealt with properly. When the shoeprints are located on a human body the challenge is greater, due to the curved shape of the human body and the skin texture. We made several dust impressions on a human volunteer. The prints were lifted using three different methods: electrostatic lifter, black gelatin lifter and white adhesive lifter followed by enhancement with Bromophenol Blue (BPB). The prints recovered on the white adhesive were screened by skin debris that reacted with the Bromophenol blue. Full contact was not achieved between curved organs and the ESL. Another disadvantage of the ESL is that the electrostatic charge might be dangerous when used on live subjects. The best method was found to be the black gelatin lifter.

Dental stone is used as the major material for recovering three-dimensional shoeprints and tire tracks from crime scenes. The procedure for using dental stone sparsely changed over the years. There are two common methods for mixing dental stone: (i) a premeasured amount of dental stone is put in a zip-lock bag to which water is added, and (ii) the water and dental stone are mixed in a bucket. We suggest a novel rapid and efficient method of mixing dental stone and water in a bottle. These methods were compared at equal conditions. The parameters measured were the number of air bubbles, the strength of the cast, the ease of use, and the sharpness and quality of the accidental characteristics present in the cast. The proposed bottle method has the advantages of both the bucket and the zip-lock methods hence it combines strength, sharpness, high quality, and ease of use.

In forensic literature a physical match is often regarded as conclusive evidence, but Daubert ruling may change this. Every layman can determine physical match, and yet the individuality of physical match was never proven scientifically. Usually, tearing conditions are irreproducible. The direction and tearing force, and the nature and thickness of the substrate may vary. These varying parameters influence the advancement of the tear. This study tests if a tear remains unique, even when the tearing process is conducted under measurable and reproducible conditions. Substrates with homogenous properties were chosen. A standardized tensile machine with set force and speed conducted the tearing. Each torn sample was composed of two rims of the tear. A portion was cut from one rim, and the experts tried to find the fitting place on the opposite rim in a “double blind” test. Results of the study show that even tearing under repetitive conditions yields a unique contour for each sample, for the chosen materials and for length greater than 1 cm. Thus, it is demonstrated that individuality of the process is due to the material's internal structure.

Gelatin lifter is widely used for recovering shoeprints from crime scenes. Dusty shoeprints removed from paper with loose fibers, cloth or plasterboard, might be concealed by the detached fibers. A novel technique to clean the gelatin lifter from the interfering contaminations, using adhesive lifters, was developed. The adhesive lifter is applied directly on the surface of the gelatin lifter, and is removed instantly. The adhesive lifter removes the upper layer of the attached material on the gelatin lifter. After removing the concealing material from the hidden imprint, the quality of the visualized imprint is improved. The cleaning process can be applied as many times as needed and the optimum number is different for each substrate. The small dust particles comprising the shoeprint remained attached to the sticky side of the gelatin lifter even though the adhesion force applied by the adhesive lifter is great. Repeating the procedure too many times could harm the quality of the print severely, yet the advantages of this method are greater than the risks of relocation of image quality reduction.

A method for lifting bloody footwear impressions using alginate casts and enhancing the lifted impressions with amido black is presented. On rough or dark substrates, background interferences may conceal significant details of footwear impressions. Illumination with alternative light sources and chemically enhancing the bloody footwear impressions may reveal additional details, but sometimes, lifting footwear impressions prior to enhancing is the only way to expose hidden details (by using blood reagents not adequate on the original). Several cast formulations were tested for lifting the footwear impressions. The best results were achieved using Aroma fine®. Enhancement of the footwear impressions was attempted with several reagents prior to lifting, during the casting process, and on the lifted footwear impressions. Applying amido black to footwear impressions lifted with alginate produced the sharpest and most detailed footwear impressions. Alginate castings followed by chemical enhancement with amido black may produce high-quality footwear impressions for comparison.

Dental stone is used as the major material for recovering three-dimensional shoeprints and tire tracks from crime scenes. The procedure for using dental stone sparsely changed over the years. There are two common methods for mixing dental stone: (i) a premeasured amount of dental stone is put in a zip-lock bag to which water is added, and (ii) the water and dental stone are mixed in a bucket. We suggest a novel rapid and efficient method of mixing dental stone and water in a bottle. These methods were compared at equal conditions. The parameters measured were the number of air bubbles, the strength of the cast, the ease of use, and the sharpness and quality of the accidental characteristics present in the cast. The proposed bottle method has the advantages of both the bucket and the zip-lock methods hence it combines strength, sharpness, high quality, and ease of use.

Two-dimensional dust shoeprints are often of very high resolution and contain unique features. Lifting these prints in the most effective method may contribute much to preserving these fine details. A research was conducted by experts from Israel and Switzerland to compare gelatin lifters and electrostatic lifters for lifting shoeprints. Several substrates were chosen, and on each material a set of dry dust shoeprints was made. A set of wet prints was made on paper as well. The shoeprints were approximately of the same quality, and the only variable was the nature of the material. On substrates indifferent to the method used, the preferable sequence was tested. Gelatin lifter was superior on most substrates and for wet prints. The superior sequence for using both methods is electrostatic lifting followed by gelatin lifter.

The compound 1,2-indanedione was recently introduced in our laboratory as an operational reagent for developing latent fingerprints on porous surfaces. As part of the reagent implementation, a study was carried out in order to determine whether either of the two operational 1,2-indanediones formulations interferes with further DNA profiling. Both formulations are based on HFE7100 solvent. One is acidic and the other neutral. In a controlled experiment, known donors attached stamps to envelopes by licking them. The stamped envelopes were initially treated with either one indanedione formulation or the other, and DNA was then extracted for STR typing. No differences were observed between the STR profiles obtained from treated and untreated stamps and envelopes, indicating that 1,2-indanedione does not adversely affect the extraction and subsequent amplification of the STRs examined. However, preliminary results indicate that potential DNA analysis depends on the time interval between the indanedione treatment and DNA extraction as no DNA can be recovered six days following treatment. For this reason, it is strongly recommended to extract DNA from treated items of evidence as soon as possible after indanedione treatment.

The performance of 1,2-indanedione as a latent fingerprint reagent on some types of paper was found to exceed that of DFO, the leading fluorogenic fingerprint reagent. It even exceeds the performance of the sequence, DFO, followed by ninhydrin. No new prints could be observed when ninhydrin was applied after indanedione. On a large number of actual exhibits (used checks) indanedione developed 46% more identifiable prints than the sequence DFO-ninhydrin. A standard procedure for fingerprint development by indanedione is proposed. Best results are obtained with a 0.2% indanedione solution in HFE7100 solvent containing 7% ethyl acetate, but no acetic acid. It can be recommended to start using 1,2-indanedione, which is already commercially available, in actual fingerprint casework.

A number of vicinal cyclic diketones, most of them belonging to the 1,2-indanedione series, have been prepared and tested as potential reagents for latent fingerprint development. Unsubstituted 1,2-indanedione and a number of its mono- and dimethoxy- derivatives exhibited excellent properties as fluorogenic reagents for latent prints on paper. Structural modifications, such as substitutions at position 3, omission of the benzene ring or increase of the five-membered to a six-membered ring, considerably reduced this activity. Quite surprisingly, benzo[f]indane-1,2-dione, which was synthesized for the first time in this work, was significantly inferior to 1,2-indanedione as a fingerprint reagent. Even at this stage, before optimization of the reaction conditions, it can be said that some 1,2-indanediones are at least as sensitive as DFO. Their solubility in nonpolar solvents and relative case of preparation are further advantages. It is the authors' opinion that 1,2-indanedione itself may soon become a practical fingerprint reagent.