Highlights
- •The contamination risk of tools used during exhibit examination was evaluated.
- •Scissors, forceps and gloves are a contamination risk, they readily transfer DNA.
- •Transfer detectability is dependent on the substrates and biological sources involved.
- •Contaminating alleles may affect the probative value of DNA profiles in casework.
Abstract
The introduction of profiling systems with increased sensitivity has led to a concurrent
increase in the risk of detecting contaminating DNA in forensic casework. To evaluate
the contamination risk of tools used during exhibit examination we have assessed the
occurrence and level of DNA transferred between mock casework exhibits, comprised
of cotton or glass substrates, and high-risk vectors (scissors, forceps, and gloves).
The subsequent impact of such transfer in the profiling of a target sample was also
investigated. Dried blood or touch DNA, deposited on the primary substrate, was transferred
via the vector to the secondary substrate, which was either DNA-free or contained
a target sample (dried blood or touch DNA). Pairwise combinations of both heavy and
light contact were applied by each vector in order to simulate various levels of contamination.
The transfer of dried blood to DNA-free cotton was observed for all vectors and transfer
scenarios, with transfer substantially lower when glass was the substrate. Overall
touch DNA transferred less efficiently, with significantly lower transfer rates than
blood when transferred to DNA-free cotton; the greatest transfer of touch DNA occurred
between cotton and glass substrates. In the presence of a target sample, the detectability
of transferred DNA decreased due to the presence of background DNA. Transfer had no
impact on the detectability of the target profile, however, in casework scenarios
where the suspect profiles are not known, profile interpretation becomes complicated
by the addition of contaminating alleles and the probative value of the evidence may
be affected. The results of this study reiterate the need for examiners to adhere
to stringent laboratory cleaning protocols, particularly in the interest of contamination
minimisation, and to reduce the handling of items to prevent intra-item transfer.
Keywords
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Article info
Publication history
Published online: February 16, 2015
Accepted:
February 12,
2015
Received in revised form:
January 29,
2015
Received:
September 24,
2014
Identification
Copyright
© 2015 Elsevier Ireland Ltd. Published by Elsevier Inc. All rights reserved.
