Measuring the water content in freshly-deposited fingermarks

The effect of handedness and biological sex on fingermark ridge height and volume as examined by 3D imaging

For decades, detectives and forensic scientists have relied on friction ridge skin comparisons to identify individuals in criminal investigations. This method involves examining (latent) fingermarks, typically captured as two-dimensional (2D) images, and comparing them with known inked impressions or scans. The comparisons focus on general patterns, the location and orientation of minutiae, and additional characteristics like scars or pores. However, this common process overlooks other potentially valuable factors, such as handedness, biological sex, and the time since deposition, which could provide crucial investigative leads, especially in cases with partial or unclear ridge patterns. This study explored the potential of three-dimensional (3D) optical profilometry (OP) to observe changes in fingermarks ridge height and volume over 7 days while considering hand dominance and biological sex. The results indicated that all the assessed 3D metrics were generally consistent in detecting the effects of sex and handedness, mostly noticeable on aged fingermarks. Specifically, females and impressions from their non-dominant hand exhibited higher values. Additionally, the influence of time was evident, with fresh fingermarks showing significantly larger ridges in terms of height and volume. These findings suggest that 3D OP can enhance the probative value of fingermarks by inferring additional characteristics such as sex, handedness, and the age of the impression. These activity-level propositions could provide useful information in cases where only partial or poor-quality fingermarks are recovered, providing new data dimensions that could lead to more comprehensive forensic examinations.

Using the refractive index of latent fingerprints for the quantification and characterisation of sample deposition

Latent fingerprints (LFPs) are predominantly used for personal identification, but in recent years research has shown their potential for drug screening. Despite this there is no standardised collection method to allow accurate drug test interpretation. We sought to help address this by characterising different variables related to sweat deposition in LFPs as the knowledge is limited. A series of experiments were conducted firstly to validate a novel tool called the Ridgeway (Intelligent Fingerprint Ltd. UK) to quantify the amount of sweat deposited from a LFP using the refractive index (RI). A significant positive correlation was observed between the Ridgeway score (Rs) and LFP mass [r = 0.868, p < 0.01]. The Rs was used as means to investigate optimal sampling to characterise sample deposition for drug screening purposes. It was found with a consistent disposition pressure (300 - 400 g) and surface (glass slide) no significant difference was observed between the left and right index finger [left: p = 0.938; right: p = 0.838]. Significantly higher Rs [p<0.01] were obtained when 10 cumulative LFPs were deposited compared to a single LFP, suggesting a larger sweat quantity. We also wanted to investigate optimal eccrine sweat sampling to confirm drug ingestion over drug contamination of the fingerprint. We found that wearing gloves did not significantly improve mean difference in Rs when compared to no gloves [p = 0.239]. To produce eccrine only LFPs, external contamination (e.g. sebaceous sweat) needs to be removed. Soap with lint free tissue was significantly better for this compared to antibacterial hand gel [p<0.01]. Our findings showed that the Ridgeway tool effectively quantified LFPs at the point of deposition using a refractive index and enabled us to establish conditions for consistent LFP sampling.

Predicting Fingerprint Age Based on Ozonolysis Kinetics of Unsaturated Triacylglycerol Degradation

Answering the question, "How old is a fingerprint?", is a highly sought-after aim in forensic science. Despite several decades of studies to find an empirical correlation in fingerprint aging, there has been no reliable method so far. In this study, we attempt to determine the time since deposition (TSD) of aged fingerprints from the chemical profile captured within a matrix-assisted laser desorption/ionization mass spectrometry data set. Our approach is based on the chemical kinetics associated with the ambient ozonolysis of unsaturated triacylglycerols (TGs), a major component in fingerprint lipids. First, ozone concentration and ambient temperature were determined to be the major factors in the degradation of unsaturated TGs. A simple kinetics model is then developed to describe the decay of unsaturated TGs, dictated only by the temperature and ozone concentration. This model is then applied to the degradation of TGs in a mixture of TG standards and multiple individuals' fingerprints. The overall decay of unsaturated TGs follows the pseudo-first-order reaction kinetics, validating our hypothesis; however, there are significant person-to-person variations in the initial abundance of unsaturated TGs and the decay rate, hampering the accurate prediction of TSD unless they are corrected for each individual. Nevertheless, the model's applicability for ambient fingerprint aging data was successfully demonstrated.

A comparison of the natural and groomed fingermark lipid composition of different donors using GC/MS

The lipid composition of natural fingermarks was studied and compared with the composition of groomed residue. Approximately 100 specimens were collected from 6 donors over three sessions (in October, December and July) and analysed using gas chromatography / mass spectrometry (GC/MS). The measured lipid content was generally lower and more variable in natural fingermarks than in groomed fingermarks. Some significant variability was noticed. Relative standard deviations were the highest between donors (generally above 100%) but were also relatively high within donor within a session (from 21% to 80%) and between sessions (from 34% to 126%). The fingermarks from one of the donors generally contained higher relative amounts of lipids in both groomed and natural residue compared to the others. All other fingermarks led to very variable amounts and did not allow classifying the other donors as constantly "good" or "poor" donors. Squalene was the major compound in all marks, particularly in groomed specimens. A correlation between squalene, cholesterol, myristic acid, palmitoleic acid, stearyl palmitoleate and pentadecanoic acid was highlighted. Oleic and stearic were also correlated together but generally more in natural than groomed marks. The obtained results may be particularly useful to better understand the detection mechanisms for techniques targeting lipids and to develop artificial fingermark secretions to further support the development of detection techniques.

Monitoring the chemical changes in fingermark residue over time using synchrotron infrared spectroscopy

Using synchrotron sourced ATR-FTIR microspectroscopy and THz/Far-IR gas phase spectroscopy to monitor the chemical changes in fingermark residues in the immediate hours following deposition.

DNA recovery after sequential processing of latent fingerprints on copy paper

Forensic examiners must determine whether both latent fingerprint development and DNA profiling can be performed on the same area of an evidence item and, if only one is possible, which examination offers the best chance for identification. Latent fingerprints can be enhanced by targeting different components of fingerprint residues with sequential chemical treatments. This study investigated the effects of single-reagent and sequential latent fingerprint development processes on downstream DNA analysis to determine the point at which latent fingerprint development should be stopped to allow for DNA recovery. Latent fingerprints deposited on copy paper by one donor were developed using three sequential processes: 1,8-diazafluoren-9-one (DFO) → ninhydrin → physical developer (PD); 1,2-indanedione-zinc (IND-Zn) → ninhydrin → PD; and IND-Zn → ninhydrin → Oil Red O (ORO) → PD. Samples were examined after the addition of each chemical treatment. DNA was collected with cotton swabs, extracted, quantified, and amplified. DNA yields, peak heights, number of alleles obtained, and percentage of DNA profiles eligible for CODIS upload were examined. DNA profiles were obtained with varying degrees of success, depending on the number and type of treatments used for latent fingerprint development. The treatments that were found to be the least harmful to downstream DNA analysis were IND-Zn and IND-Zn/laser, and the most detrimental treatments were DFO, DFO/laser, and PD. In general, as the number of treatments increase, the opportunities for DNA loss or damage also increase, and it is preferable to use fewer treatments when developing latent fingerprints prior to downstream DNA processing.

To glove or not to glove? Investigations into the potential contamination from handling of paper-based cultural heritage through forensic fingerprinting approaches

The handling of cultural heritage objects has become a highly debated topic in the last decade. The work and outcomes described in this paper are aimed to provide objective data to assist in making appropriate decisions as to whether or not wearing gloves is appropriate in a given situation. The forensic fingermark development techniques of 1,2-indandione and single metal deposition II were used to investigate the efficacy of handwashing and glove use to improve the information available when deciding whether to use gloves when handling paper objects. It was found that fingermarks did not permeate through polymer glove types but could through cotton gloves. It was also shown that the amounts of observable fingermark residues were greater 5 min after handwashing than if handwashing had not occurred, undermining previous arguments for not wearing gloves if hands could be washed before object handling.

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Fingermarks can be transferred onto paper even after washing hand.

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Developed fingermark residues initially increase after handwashing.

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Handwashing is not sufficient to prevent fingermark contamination of artifacts.

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Fingermark residues can be transferred from surfaces to gloves to paper.

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Some antibacterial gels can increase the amount of fingermark residue deposited.

Interpol review of fingermarks and other body impressions 2016-2019

This review paper covers the forensic-relevant literature in fingerprint and bodily impression sciences from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20 Review%20 Papers%202019. pdf.

Methodologies Applied to Fingerprint Analysis

This systematic review deals with the last 10 years of research in analytical methodologies for the analysis of fingerprints, regarding their chemical and biological constituents. A total of 123 manuscripts, which fit the search criteria defined using the descriptor "latent fingermarks analysis," were selected. Its main instrumental areas (mass spectrometry, spectroscopy, and innovative methods) were analyzed and summarized in a specific table, highlighting its main analytical parameters. The results show that most studies in this field use mass spectrometry to identify the constituents of fingerprints, both to determine the chemical profile and for aging. There is also a marked use of mass spectrometry coupled with chromatographic methods, and it provides accurate results for a fatty acid profile. Additional significant results are achieved by spectroscopic methods, mainly Raman and infrared. It is noteworthy that spectroscopic methods using microscopy assist in the accuracy of the analyzed region of the fingerprint, contributing to more robust results. There was also a significant increase in studies using methods focused on finding new developers or identifying components present in fingerprints by rapid tests. This systematic review of analytical techniques applied to the detection of fingerprints explores different approaches to contribute to future studies in forensic identification, verifying new demands in the forensic sciences and assisting in the selection of studies for the progress of research.

Clean and clear (out): A neat method for the recovery of latent fingermarks from crime-scenes

Crime-scenes are the heart of any investigation in terms of recovery of key forensic evidence - fingermarks and DNA. Yet, quite often, the operational work of the forensic units, in which different chemicals and reagents for fingermarks development are applied, can also be highly destructive to the property and the environment. Hence, for both ecological and intelligence purposes, an operational method that minimizes that damage would be ideal. In this study, an "out-of-the-box" approach is proposed; rather than working at the crime scene itself, gel-lifters were used as a transferring tool for the latent forensic evidence, fingermarks and DNA, to be developed by applying black wet-powder (Wetwop®) in a controlled laboratory environment, leaving the crime-scene undisturbed. The results show a promising potential, as this indirect method proved to be robust and successful for non-porous surfaces, and even for aged fingermarks. In addition, this study gave a new perspective into the accepted notion regarding the difference between male and female donors, showing a direct correlation of the size and weight of the hands to the natural pressure applied by the donor. Moreover, the indirect nature of the method highlights the importance of the interaction between the type of surface and the latent fingermark constituents, primarily water, and its effect on the survivability and quality of the developed fingermark. Due to the growing demand of keeping crime scenes and exhibits unharmed by both police and intelligence forces, the new approach of this application provides a valuable asset for future operational field-work.