Examination of Firearms Review: 2007 to 2010 - Interpol

triethylamine and ethanolamine vapors prior to cyanoacrylate fuming leads to much
more effective fingermark detection. Nevertheless, an increase of the background
staining has been observed, especially if the evidence has not been exposed to acid
environment prior to the basic pretreatment. Physical enhancement techniques (e.g.,
powder dusting or small particle reagents) could successfully be applied on the
acidified substrates without any pretreatment step, but there is a risk that increased
background staining occurs.
Biological contamination
Hoile et al. proposed to modify a decontamination protocol based on the use of
formaldehyde, which acts like a biocidal/sporicidal agent and which is generally used
in the case of biological contaminations (e.g., anthrax spores) (315). When dealing
with an item suspected to have been contaminated with biological agents, a common
decontamination procedure consists in using formaldehyde vapour for six to 12
hours. This treatment results in the destruction of the spores, but also to a
degradation of the amino acids present in the latent residue. Hoile et al. studied the
effect of this decontamination procedure on some commonly used fingermark
detection techniques (i.e., ninhydrin, DFO, 1,2-indanedione, physical developer,
cyanoacrylate, and powders). For this study, fingermarks were left on glass and
paper substrates, which were put in contact with formaldehyde vapors from 10
minutes to 12 hours. If cyanoacrylate fuming, powdering, and physical developer
continued to be successfully applied after the decontamination procedure, this was
not the case with ninhydrin, DFO, and 1,2-indanedione which failed to detect latent
marks. Hoile et al. revised the decontamination procedure by reducing the
concentration of formaldehyde and the exposure time (i.e., 40 minutes instead of six
to 12 hours), which resulted in 66%, 33%, and 8% successful recovery rates for
ninhydrin, DFO, and 1,2-indanedione, respectively.
The impact of bacterial agents on the efficiency of the classical fingermark detection
techniques has been studied by Wilkinson et al. (317). For this study, various porous,
non-porous and adhesive substrates were considered (e.g., plastic, glass, cardboard,
metal, paper, tapes) on which latent and blood fingermarks were left. A high number
of fingermarks (ca. 400) from eight donors were used, and were aged for one to
seven days prior being exposed to the bacterial agents. The samples were
contaminated with bacterial cultures for 24 to 48 hours, before being processed with
classical fingermark detection reagents (i.e., DFO, ninhydrin, amido black, Hungarian
red, leucomalachite green, powder suspension, cyanoacrylate fuming, and dry
powders). The authors observed no effect of the bacterial exposure for porous
exhibits (100% trace recovery), and a minor effect on nonporous substrates (97%
trace recovery for cyanoacrylate). Blood reagents reacted quite well, with a rate of
recovery between 86 and 97%. Only the adhesive items showed varied results. In
addition to these observations, the bacterial exposure time (from 24 hours to 48
hours) and the age of the fingermarks (from one to seven days) seemed to have no
effect on the recovery rates.
Hoile et al. investigated the use of gamma irradiation (25 to 40 kGy using cobalt-60
as irradiation source) to decontaminate spore-contaminated evidence, and its effect
on the subsequent fingermark detection techniques, as well as on the recovery of
human DNA (316). Different substrates were considered (i.e., paper, cardboard,
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