Examination of Firearms Review: 2007 to 2010 - Interpol

glass, and plastic) on which fingermarks from three donors were left. After having
been exposed to irradiation doses from 200 Gy to 5 kGy, the items were processed
using common detection techniques (i.e., ninhydrin, DFO, 1,2-indanedione, physical
developer, cyanoacrylate and dry powders). Preliminary tests on microbial colonies
showed that a gamma dose of more than 3 kGy should be used to decontaminate
evidence. As observed by Colella et al. (318), glass underwent some discolouration
(browning) above 1 kGy without interfering with the quality of the fingermark
detection process. No adverse effect due to irradiation (in terms of ridge details) was
observed for the processing of the porous and non-porous substrates, even for a 40
kGy irradiation dose. This observation is in agreement with the results obtained by
Colella et al.. About DNA profiling, the quantity of DNA recovered could be affected
by the irradiation process, but the possibility to recover human DNA from paper, post
gamma irradiation, is not excluded even up to 50 kGy doses (more severe
degradation occurs above this value).
Radiation
Colella et al. investigated the possibility to recover latent fingermarks from evidence
that was exposed to ionizing radiation (318). Common surfaces were considered
(i.e., aluminium, glass, office paper, and plastic), on which fresh and good
fingermarks were left, before being irradiated to doses from 1 to 1000 kGy (which
constitutes significantly higher exposure doses compared to the electron beam
irradiation used to sanitize mail). A cobalt-60 ionization source was placed at one, 10
and 100 mm of the substrates, and exposure times ranged from 24 hours to seven
days. Common detection techniques were considered (i.e., cyanoacrylate with dye,
black powder, ninhydrin, DFO, 1,2-indanedione, and physical developer). It was
concluded that radiolysis had a considerable effect on the quality of the developed
fingermarks, at the exception of marks on glass and aluminium which showed no
influence due to the ionization process. With respect to glass, the irradiation caused
an optical degradation of the substrate which became deep brown as the ionizing
dose increased. Nevertheless, this effect had no impact on the detection of
fingermarks (the only detrimental effect would be in terms of reduced contrast). For
the other substrates, the irradiation caused physiochemical and mechanical damage
in the inner structure of the material (e.g., plastics) especially for doses above 100
kGy. This resulted in unwanted polymerization sites or background fluorescence, in a
degradation of the substrate mechanical properties preventing them to be properly
processed (e.g., paper), or in a chemical modification of the secretion residue making
them less prone to react. Nevertheless, up to 100 kGy, it has been shown that the
processing of latent fingermarks using common detection techniques is still possible.
Parkinson et al. investigated the efficiency of two decontamination procedures used
in case of irradiated documents, and their impact on fingermark detection techniques
and ink analysis (319). Three irradiation sources were used (i.e., cesium-137,
americium-241, and strontium-90) to contaminate paper samples that were
subsequently processed for fingermark detection (using DFO, ninhydrin, 1,2indanedione,
and physical developer). After the detection of fingermarks, the
substrates were decontaminated by following a physical process (scraping of the
surface with a scalpel followed by the use of a pencil eraser) or a chemical one
(immersion of the evidence from 0 to 30 minutes in a sonication bath containing
water or cyclohexane, and DEZ-1 - a complexing agent used as a decontaminant).
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