Effect of substrate surface topography on forensic development of latent fingerprints with iron oxide powder suspension

Abstract

Latent fingerprint deposition and effectiveness of detection are strongly affected by the surface on which prints are deposited. Material properties, surface roughness, morphology, chemistry and hydrophobicity can affect the usefulness or efficacy of forensic print development techniques. Established protocols outline appropriate techniques and sequences of processes for broad categories of operational surfaces. This work uses atomic force microscopy and scanning electron microscopy to investigate a series of surfaces classified as smooth, non-porous plastic. Latent prints developed with iron oxide powder suspension are analysed on a range of scales from macro to nano to help elucidate the interaction mechanisms between the latent fingerprint, development agent and underlying surface. Differences between surfaces have a strong effect, even within this single category. We show that both average roughness and topographical feature shape, characterized by skew, kurtosis and lay, are important factors to consider for the processing of latent fingerprints.The pre-peer review version of this article is included in the following pages. Please access the publisher's website for the definitive version Effect of Substrate Surface Topography on Forensic Development of Latent Fingerprints AbstractLatent fingerprint deposition and effectiveness of detection are strongly affected by the surface on which prints are deposited. Material properties, surface roughness, morphology, chemistry and hydrophobicity affect the usefulness or efficacy of forensic print development techniques such as dry powder, powder suspension, cyanoacrylate fuming or vacuum vapour deposition, and lack of development agent adhering to deposited print as well as excess background staining are both problematic. The deposited fingerprint is further affected by the contact conditions and the individual donor. Additional factors affect the detection algorithm such as pre-and post-deposition environment of the surface, humidity, contamination and cleaning agent or solvent spray.This work uses atomic force microscopy and scanning electron microscopy to investigate a series of surfaces and the interaction between latent fingerprint, surface and development agent. Latent prints developed with various techniques are analysed on a range of scales from macro-to nano-to help to elucidate the mechanisms of fingerprint development and aims to aid detection technique enhancement and algorithm improvement.

Nanoscale Analysis of the Interaction Between Cyanoacrylate and Vacuum Metal Deposition in the Development of Latent Fingermarks on Low‐Density Polyethylene*

“…These analyses indicate zinc nanoparticle decoration of polycyanoacrylate fibrils, as well as zinc deposition associated with areas of fingermark ridges away from effective CA development. This process may relate to the improved definition of the print seen in other works (2,5,11) through zinc deposition on the nodular structure formed by superficial CA treatment, without extended polymerization. This appears to aid VMD but does not assist with contrast development with the CA process and would not interact with dyeing agents in the same manner as the polymer chains.…”

“…Initial examination shows that CA fuming produces polymerized CA mainly focused around pores in the latent fingermark. The application of gold and zinc through a VMD technique to a sample previously treated with CA causes the development of additional areas not coated with polycyanoacrylate, which relates to the improved definition of the print seen in other works (2,5,11). However, the primary interaction of the zinc deposition appears to be with the polycyanoacrylate, decorating the polymer chains with nanoscale particulates.…”

“…Depletion series of 10 natural prints were collected from each donor. Utilizing a similar process to an earlier study (11), no grooming procedure for loading with sebaceous or eccrine material was applied, although donors were asked not to have washed their hands for at least 30 min before donation. Variability was minimized by lightly rubbing fingertips together prior to deposition.…”

Quantitative Scanning Probe Microscopy for Nanomechanical Forensics

“…For example, the initial residue composition (point 1) is a combination of numerous substances from the epidermis [49], dermis [50], and extrinsic contaminants [51], with the exact properties dependent on the ratio of the three components [48]. Moreover, on point (3), it has been found that the porosity [52] and roughness [18] of the surface influence the composition and aging kinetics of a fingerprint, as they determine the adsorption rates of the water-soluble compounds in the residue and the effectiveness of the print detection scheme, respectively. As a result of the many confounding factors that contribute to the final characteristics of the print, it is necessary to utilize methods that both “look” and “feel” the print surface, as they not only provide information regarding the print’s owner, but also insight into the print’s composition and age.…”

“…AFM images have revealed sizeable variations in the morphology of various viruses and bacterial spores, and how these variations change with the nutrient exposure [16]. AFM images have been used to image fingerprint residue [17] and powder spray [8] and to set the baseline structures of polymeric [18] and metallic [19] surfaces employed in latent fingerprint development. Statistical analyses of AFM topography measurements of textile fibers exposed to environmental stress were used to illustrate the ability of nanoscale images to distinguish different environmental exposures [20].…”