Examination of Firearms Review: 2007 to 2010 - Interpol

indicating that care must be taken when comparing samples taken from the
suspects or victims and cartridge cases. This, of course is true on a purely
quantitative level – it is clear that the elemental composition of the particles is still
in agreement.
3.1.5 Quality
Due to international requirements (e.g. ENFSI) or national legislations, Quality
assurance is more and more implemented in GSR laboratories, with a crucial
step consisting of the accreditation of the analysis method following the ISO
17025 norm. In reference (125) are discussed the type of documents that have to
be prepared for this accreditation. Repeatability, reproducibility, robustness and
interlaboratory tests are illustrated using an example of validation framework.
Some Quality assurance considerations are also discussed when a new
SEM/EDX equipment has to be acquired; on-site demonstration tests and
selection criteria are proposed.
Besides instrumental validation, other topics have to be examined for complete
validation of GSR identification using SEM/EDX. Kopina (126) present a
validation study including i) the characterization of GSR (composition and
morphology) coming from 83 different ammunitions, ii) the effectiveness of
sampling using different types of adhesives, and iii) the influence of time and
activity after shooting. As a result of this validation, the load factor (amount of
consistent particles per square millimetre of analysed sample) is introduced with
a discriminating threshold value in order to distinguish background from potential
discharge samples. Four classes are defined for each hand sample: unique and
consistent, consistent, hand background, and contaminated (using a control
sample).
Proficiency tests are conducted every 2-3 years. They are organised by the
ENFSI Expert Working Group "Firearms" and consist of the detection by
SEM/EDX of 100 three-element particles (lead, barium and antimony) distributed
in four size classes (0.5 µm, 0.8 µm, 1.2 µm and 2.4 µm). Two proficiency tests
were conducted during the period of interest (GSR2008 and GSR2010). The
results have been (GSR2008) or will be (GSR2010) discussed during dedicated
workshops. Moreover, the results of the GSR2005 proficiency test were
published (127). Compared to the previous test (GSR2003 (128)), more
laboratories participated and about one fourth of them were non-European
laboratories (mostly USA). The comparison of the z-scores of the two tests
revealed an improvement of the detection capability of the laboratories. Moreover
the results are on average better for the laboratories that took part in the two
series, leading to the conclusion that a continuous participation in the proficiency
test program contributes to an improvement in the individual performances.
31