Abstract
This study thoroughly explores the use of time-of-flight secondary ion mass spectrometry (ToF-SIMS) for determining the deposition sequence of fingermarks and ink on a porous paper surface. Our experimental work has demonstrated that mapping selected endogenous components present in natural fingermarks enables the observation of friction ridges on a laser-printed surface, only when a fingerprint is deposited over this layer of ink. Further investigations have shown limited success on ink-jet printing and ballpoint pen inks. 51 blind tests carried out on natural, latent fingermarks on laser-printed surfaces; up to 14th depletion with samples aged for up to 421 days have resulted in a 100% success rate. Development with ninhydrin was found to affect the fingermark residue through mobilisation of ions, therefore sequencing determination was compromised; whilst iodine fuming and 1,2-indanedione developers did not. This implied that selected development methods affected success in fingermark-ink deposition order determination. These results were further corroborated through inter-laboratory validation studies. The adopted protocol and extensive series of tests have therefore demonstrated the effectiveness and limitations of ToF-SIMS in providing chronological sequencing information of fingermarks on questioned documents; successfully resolving this order of deposition query.
Highlights
IntroductionWhen investigating cases of fraud or counterfeiting, besides recovering the ngermark ridge pattern on a handled document, it is necessary to establish whether the ngerprint has been deposited before or a er the surface was written or printed over with compromising ink material
Fingerprint evidence is routinely used in forensic investigations and has been a widely accepted form of identi cation evidence for over 100 years.[1]
In our research we explore the application of timeof- ight secondary ion mass spectrometry (ToF-SIMS) as a suitable technique to establish the chronological sequence of printed inks and ngermarks on paper
Summary
When investigating cases of fraud or counterfeiting, besides recovering the ngermark ridge pattern on a handled document, it is necessary to establish whether the ngerprint has been deposited before or a er the surface was written or printed over with compromising ink material. In our research we explore the application of timeof- ight secondary ion mass spectrometry (ToF-SIMS) as a suitable technique to establish the chronological sequence of printed inks and ngermarks on paper This instrumental method targets the chemical composition of a sample, providing a combination of elemental and molecular fragment signatures which can be directly linked to individual constituents within a sample complex. When coupled with a time-of- ight mass spectrometer, this instrumental method allows for rapid mass-spectral analysis over a wide mass range with good mass resolution It is capable of producing high resolution chemical images by rastering the ion beam across the sample surface.[17] ToF-SIMS has excellent lateral resolution capabilities, is surface sensitive, and has recently demonstrated applications in the forensic analysis of ngerprints,[18,19,20,21] papers and paper coatings,[22] and in determining the deposition order of ngerprints and ball point inks, with limited success.[18,23]. This work advises the order of which latent ngermarks should be developed on this type of evidence to effectively target the deposition order query
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