PAPER CRIMINALISTICS Josep De Alcaraz-Fossoul, 1 Ph.D.; Carme Barrot Feixat, 2 Ph.D.; Clara Carreras-Marin, 2 M.Sc.; Jack Tasker, 2 B.Sc.; Sara C. Zapico, 3 Ph.D.; and Manel Gen e Badia, 2 Ph.D. Latent Fingermark Aging Patterns (Part III): Discontinuity Index as One Indicator of Degradation ABSTRACT: This article is the third in a series of reports exploring quantifiable visual parameters of the aging process of latent finger- marks. On this occasion, research is focused on the occurrence of ridge discontinuities (i.e. breakages) as a function of time. Experiment vari- ables included type of secretion (eccrine and sebaceous), substrate (glass and plastic), and exposure to natural light (dark, shade, and direct light) over a 6 months period. Fingermarks were sequentially visualized with titanium dioxide powder, photographed, and the number of natu- rally occurring ridge discontinuities subsequently evaluated. A semi-quantitative value, named Discontinuity Index, was used to better character- ize this aging parameter. Results indicated that ridges of sebaceous depositions on glass were generally less affected by the environmental conditions compared with those on plastic surface. In addition, aging in darkness was not always the best condition for preservation, and the direct exposure to light seemed not to affect the degradation under certain conditions. KEYWORDS: forensic science, aging, discontinuities, latent fingerprint, dating, titanium dioxide, parameters, morphometrics Latent fingermarks have been commonly used for the identifi- cation of crime suspects and victims by forensic laboratories for over a century (1). During this time, a large number of experi- mentations and investigations have been conducted to understand the chemical and physical characteristics of this type of evi- dence. In the past few years, and despite limited financial resources, several forensic institutions have been exploring meth- ods to examine the chemical and physical changes that occur during the degradation process with the ultimate goal to deter- mine the aging patterns and/or the actual age of a latent finger- mark left behind at a scene (2,3). Currently, there exist two different approaches to study the aging process of latent fingermarks. The first one is the analysis of the chemical composition of the trace that focuses on the changes of its different organic/inorganic components (4), regardless of the visual quality of the mark. The second one is the physical analysis, which uses visual methods (5), such as morphometrics (6,7) or chemical imaging (8). For the latter group, the visual quality of the deposition is a key factor for the study and the results obtained can be easily correlated with tradi- tional identification methods (i.e. minutiae comparison). Both approaches are obtaining limited but satisfactory conclusions (2). Physical analysis (i.e. morphometrics) is the method the authors of this report are developing with the objective to elucidate the degradation process (i.e. aging patterns) of latent fingermarks. The most remarkable advantages of morphometrics over chemi- cal analyses are the inexpensive equipment and consumables required. In previous articles, the authors have determined the existence of distinctive visual degradation processes of latent fingermarks from a single individual by monitoring different environmental parameters (exposure to light, temperature and humidity), type of secretion (eccrine-rich or “sweaty” and sebaceous-rich or “greasy”) and type of substrate (glass and plastic) (4). After the first publication, a project was designed to investigate the aging of latent fingermarks based on a series of visual parameters of degradation: (i) number of minutiae (9); (ii) color contrast between ridges and furrows (10); (iii) number of discontinuities; and (iv) width of the ridges. Each parameter is being studied and described individually in different articles given the large quantity of numerical data obtained. In this paper, the visual parameter discussed is the occur- rence of ridge discontinuities, which the authors have called Discontinuity Index (DI). The term “discontinuity,” for the purpose of this research, refers to the naturally occurring inter- ruptions of the ridges that “appear” during the aging process of the mark, possibly caused by the undergoing intrinsic chemical degradation of the components of the ridge. The observation of this phenomenon is thought to also be depen- dent on the level of sensitivity of the developer. In our partic- ular case, these interruptions become apparent only after visualizing the mark with a Titanium dioxide (TiO 2 )-based powder which will not bind to these degraded ridge locations. 1 New College of Interdisciplinary Arts and Sciences, School of Mathemat- ical and Natural Sciences, Arizona State University, 4701 West Thunderbird Road, Glendale, AZ 85306. 2 Legal Medicine Unit, Faculty of Medicine, University of Barcelona, C/Casanova 143, 08036 Barcelona, Catalonia, Spain. 3 Department of Applied Forensic Sciences, Mercyhurst University, 501 East 38th Street, Erie, PA 16546. Received 8 Aug. 2016; and in revised form 21 Dec. 2016; accepted 22 Dec. 2016. 1 © 2017 American Academy of Forensic Sciences J Forensic Sci, 2017 doi: 10.1111/1556-4029.13438 Available online at: onlinelibrary.wiley.com