Examination of Firearms Review: 2007 to 2010 - Interpol

fingermark detection powders prior to the Raman analysis did not interfere with the
detection and identification of the contaminants, it however increased the time taken
to locate the exogenous material due to the physical presence of more material
within the fingermark (four to five fold increase of time). Special care should be taken
when choosing the lifting tapes since interfering Raman bands coming from the lift
are to be avoided. Successful imaging of the sample through transparent evidence
bags was performed, meaning that the items do not have to be removed from such
bags to be examined. This consequently reduces contamination risks, and allows
preserving the chain of evidence.
Emmons et al. used Raman chemical imaging to detect and identify explosives (as
trace contaminants) in contaminated fingermarks (320), as described in the “CBRNErelated
evidence” section.
Raman spectral mapping was used on tape-lifted fingertips to extract chemical
information about sebum or contamination drug particles (356). For this study, one
donor was asked to rub his fingers on his forehead, or to touch drug mixtures
(containing ibuprofen, arginine and sodium bicarbonate for a first one, and sucrose
and aspartame for a second one), before a Scotch tape was applied directly on his
fingertips to lift a fingermark. These tapes were further imaged by Raman. Scanned
areas were of 200 x 200 µm² for sebum-rich marks, and of 400 x 400 µm² for the
drug-contaminated samples, which is too small to image a whole ridge pattern but
sufficient to identify the contaminants. Advanced multivariate data analysis of the
spectra was however necessary to overcome the overwhelming contribution of the
tape on the spectra, and to be able to identify the trace components (sebum or drug).
2.3.4 Miscellaneous imaging techniques
Several other techniques were developed with a common aim: imaging the
ridge patterns according to chemical or physico-chemical behaviour.
However, these techniques are still seldom used compared to FTIR and
Raman, mainly due to (1) the scanned area being too small to image a
whole ridge pattern, (2) labor-intensive methods requiring too specific
equipment. Therefore, most of the contributions constitute only preliminary
studies that may be further investigated before considering casework
application. These imaging techniques, briefly described below, are based
on: scanning electrochemical microscope (358-361), electrochromic
enhancement (362), tomography (363), surface roughness and refractive
index (364), mass spectrometry (365), time-resolved luminescence (366),
MALDI-ToF-MS (367), ToF-SIMS (368), scanning probe microscopy (369),
MALDI-MS (370), and SALDI-ToF-MS (258-260).
Scanning Probe Microscopy (SPM) was used to analyse latent fingermarks left on
glass slides (369). The scanned area was 40 x 40 µm², which is insufficient to image
a whole fingermark. The authors proposed the use of the “step-and-scan” mode that
permits to enlarge the scanned area by generating a mosaic composed of 40 images
of 70 x 70 µm². Nevertheless, this is still insufficient to distinguish ridge patterns.
Attempts to analyse superimposed fingermarks was also illustrated.
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