Fingermarks are formed from endogenous components, such as sweat from sebaceous and eccrine glands, and may include exogenous contamination, such as beauty products or residues of materials that have been recently handled. Also known as latent fingerprints, fingermarks are generally invisible until developed or otherwise visualised. Some areas of work may also include already (partially) visible patent and plastic marks, such as in blood, oil or clay; or use inked or electronically read fingerprints, recorded from the donor.
Knowledge of fingermarks can be traced back many centuries (Grew, 1684), and they remain one of the most widely used forensic identification techniques (Bleay, 2014). Generally accepted as unique and immutable, fingerprint patterns enable personal identification and can be used to link crime scene to potential suspect, or suspect to database. Fingermarks are identified, or distinguished, using information at a range of scales, including overall ridge flow, minutiae such as ridge endings and bifurcations, and pore structure within ridges. A number of research areas cover interpretation and analysis, quality assessment, comparisons of marks, and the interaction between the movement of the finger and the deposition of the mark on the substrate (Fritz et al., 2015; Fieldhouse and Gwinnett, 2016; Hockey et al., 2021; Bonnaz et al., 2021; Hanna et al., 2023).
Visualising fingermarks
Improving ways to visualise fingermarks stimulates many ongoing areas of investigation. As well as reduction in cost and improvement in speed and efficiency, these areas include understanding substrate effects, so that effective visualisation of fingermarks is maintained and improved as materials encountered at potential crime scenes vary. This may be visualisation of marks on new or complex surfaces, such as novel polymers, banknotes, gun cartridges or thermal papers (Girelli et al., 2015, Sherriffs et al., 2020, Jones et al., 2022, Woodward et al., 2023). Improvement or replacement of fingermark development formulations is also required as more information on environmental effects becomes evident, with regulations restricting solvents or other components of previously used formulations. More environmentally friendly visualisation processes, including alternative light sources and solvent-free development, help reduce impact on global warming or damage to the ozone layer, but require development and validation (Downham et al., 2018, Lee et al., 2022; Klemczak et al., 2022).
Fingermarks and efficacy of mark development techniques are also affected by the environment to which mark has been exposed. This may be weather related, or connected to the scene such as fire or immersion in water (Wightman et al., 2015; McMorris et al., 2019; Said et al., 2021).
In addition to the ridge structure and identification of pattern, the chemistry of the deposited fingermark is also important. There are differences in mark chemistry between fingermark donors and differences between marks deposited by the same donor at different times. This inter- and intra-donor variation can be a confounding factor in analysis and interpretation, but can also be advantageous in telling investigators more about the mark or the person (Bailey et al., 2012; Kent, 2016; Dorakumbura et al., 2019; Frick and Weyermann, 2019).
Intelligence from fingermarks
As well as being a form of identification, fingermarks can also help provide additional intelligence from scenes. This can include trace evidence recovery, for example after handling drugs, explosives, or condoms (van Helmond et al., 2019; Amin et al., 2022). Fingermark structure and chemistry can potentially be used to help provide information on donor characteristics, such as sex and age, and habits such as smoking or drug use (Huynh et al., 2015; Marshall et al., 2021; Bury et al., 2022; Amin et al., 2023). As well as relevance to forensic investigation, examination of donor characteristics in fingermarks has led to the potential use of fingermark chemical analysis as a screening technique for breast cancer (Russo et al., 2023).
A key aspect of forensic investigation can be to establish a timeline of events. A number of approaches are proposed to help ascertain the time from deposition of the fingermark, which may use mark chemistry, physical ridge structure, or a combination of these (Weyermann and Ribaux, 2012; Popov et al., 2017; De Alcaraz-Fossoul et al., 2021; Chen et al., 2023). Placing fingermarks in context with other evidence, such as writing or printing (Attard-Montalto et al., 2013; King et al., 2022) can also aid the understanding of the sequence of events.