Examination of Firearms Review: 2007 to 2010 - Interpol

efore powdering them (while still cold) could help in detecting latent
fingermarks (298). Finally, a comparative study was performed between
four commercially available white powder suspensions (244).
Molina tested the effectiveness of Un-du to separate stuck adhesives, and its effect
on the subsequent detection techniques (i.e., gentian violet, Sticky-side Powder, and
Wetwop) (296). Fingermarks were left on eight brands of adhesives and one selfadhesive
stamp, which were further stuck on white paper and ironed for 2-3 minutes
to induce immediate adhesion. Un-du was subsequently applied before the samples
were processed. The results showed that excessive amount of Un-du could cause
detrimental effects on the adhesive backings. All attempts provided latent
development, but the best results were obtained by combining Un-du with Wetwop, if
the latter was rinsed immediately after its application to avoid severe and irreversible
background staining (this procedure could be repeated if required).
The use of cold to help in detecting fingermarks on adhesives has been studied by
Cramer & Glass (298). The study consisted in freezing (5.5°C) four types of
adhesives (i.e., duct, clear packing, scotch and electrical tapes) bearing fingermarks
for one to 120 minutes before being dusted immediately with black or magnetic
powder. Successful detection was obtained in each case. Nevertheless, it seems that
the operator was not experienced with fingermark powdering (according to the
authors), leading to difficulty in evaluating the results at the beginning of the
experiment, and no comparisons were made between frozen and non-frozen
samples to really assess the role played by the freezing of the samples.
Bergeron conducted a study about the use of liquid nitrogen to separate adhesive
tapes that have stuck together (297). Considering 20 different brands of tape, the
author succeeded in separating stuck adhesives after having submersed the tapes
for 30 seconds in liquid nitrogen, followed by the detection of latent fingermarks using
Sticky-Side Powder once the adhesives were brought back to room temperature. It
should be noted that some difficulties could be encountered with some adhesives
(e.g., no separation or breaking of the adhesive into pieces). The author also studied
the effect of environmental conditions (e.g., heat, rain, humidity) with samples aged
up to 36 days. When the samples were protected from extreme conditions (e.g., kept
in laboratory), successful results could be obtained, even after 36 days.
Nevertheless, when subjected to outdoor environments, the likelihood of finding
latent marks was poor after a few days. Another interesting observation was made: a
mirror image of a mark could be detected on the opposite adhesive side (i.e., the one
that was stuck on the fingermark). This should be kept in mind.
As described in a previous section, Jones et al. reported an analytical study in which
they compared different white powder suspensions (i.e., TiO2 grade RG-15 -
StanChem, Wet Powder white – Kjell Carlsson Innovation, Wetwop white – Armor
Forensics, and Adhesive side Powder light - Sirchie) used to detect fingermarks on
black insulating tape, and tried to explain the differences of quality in terms of
chemical coating (244).
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