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<h4>My New Scientist</h4>
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<p>Just think of the possibilities when currency is handled by many people.</p><p><br></p><p>________________________________________________<br><span class="separator"></span><span class="separator"></span><span class="separator"></span>
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How DNA contamination can affect court cases
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13 January 2012
by
<a href="http://www.newscientist.com/search?rbauthors=Linda+Geddes"><b>Linda Geddes</b></a>
</li><li>Magazine issue <a href="http://www.newscientist.com/issue/2847">2847</a>. <a href="http://subscribe.newscientist.com/bundles.aspx"><b>Subscribe and save</b></a></li><li>
For similar stories, visit the
<a href="http://www.newscientist.com/topic/crime-and-forensics"><b>Crime and Forensics</b></a>
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<img src="http://www.newscientist.com/data/images/ns/cms/mg21328475.000/mg21328475.000-1_300.jpg" alt="Handle with care <i>(Image: Anthony Devlin/PA Wire/Press Association)</i>" title="Handle with care <i>(Image: Anthony Devlin/PA Wire/Press Association)</i>">
<p class="lowlight">Handle with care <i>(Image: Anthony Devlin/PA Wire/Press Association)</i></p>
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<p class="infuse">A WOMAN is found strangled and
partially burned in her house. DNA matching her ex-partner - who claims
he hasn't seen her for several months - is lifted from her pyjamas. The
man claims his DNA must have got there via their child's clothing or
toys. Would you believe him? Read on before reaching your decision.</p>
<p class="infuse">The conviction last week of Gary
Dobson and David Norris for the murder of Stephen Lawrence in the UK in
1993 has thrown the forensic analysis of so-called "touch" evidence into
the spotlight. The case hinged on tiny fragments of blood, hair and
fibres found on Dobson's clothes. The defence team argued that the
fragments, which were fewer in number than would be needed to fill a
teaspoon, could have got there by contamination. The forensic scientists
who testified dismissed such contamination as highly unlikely.</p>
<p class="infuse">Although there was additional evidence
against Dobson and Norris that helped to secure their conviction,
several new studies illustrate that <a href="http://www.newscientist.com/article/dn18215-knox-murder-trial-evidence-flawed-say-dna-experts.html">contamination</a>
is an issue that should be given more consideration than suggested by
the prosecution. The research shows the need for caution when
interpreting touch evidence - particularly as it becomes used more
widely.</p>
<p class="infuse">"Police are increasingly trying to
find these invisible stains, because so far as they're concerned, DNA is
a very cost-effective crime-solver," says Allan Jamieson of the <a href="http://www.theforensicinstitute.com/" target="nsarticle">Forensic Institute</a>
in Glasgow, UK. "The finding of someone's DNA implies their presence.
But presence is not a necessary consequence of finding someone's DNA."</p>
<p class="infuse">Mariya Goray of Victoria Police
Forensic Service Centre in Australia and her colleagues re-enacted
several scenarios loosely based on real events in which DNA from a
defendant was found on a victim's clothes or a murder weapon, and where
the defence argued that it could have got there indirectly. Mimicking
the scenario described in the intro, Goray asked a volunteer to handle a
child's vest and wooden toy for 1 minute before these objects were
rubbed against the front of a lab coat, which represented pyjamas. They
found that enough of the volunteer's DNA transferred to clearly identify
him (<i>Legal Medicine</i>, <a href="http://dx.doi.org/10.1016/j.legalmed.2011.09.006" target="nsarticle">DOI: 10.1016/j.legalmed.2011.09.006</a>).</p>
<p class="infuse">In a separate study, Goray and
colleagues illustrated how easily DNA can transfer within and between
items from a crime scene during transport to the lab, in a study
involving objects such as used cigarette butts and bloodied knives (<a href="http://www.sciencedirect.com/science/article/pii/S1872497311000810" target="nsarticle"><i>Forensic Science International Genetics</i>, DOI: 10.1016/j.fsigen.2011.03.013</a>).
"There is a distinct possibility for the misinterpretation of a result
that could impact negatively on the criminal investigation," says Goray.</p>
<p class="infuse">Problems may also arise when evidence
or bodies are examined on supposedly clean laboratory surfaces. Thorsten
Schwark at the University Hospital of Schleswig-Holstein in Kiel,
Germany, and his colleagues swabbed the shoulders and buttocks of six
cadavers after they had rested on autopsy tables. They found that four
of them were contaminated with DNA from bodies that had previously
rested on the table - in two cases with DNA from more than one person (<i>Forensic Science International</i>, <a href="http://dx.doi.org/10.1016/j.forsciint.2011.09.006" target="nsarticle">DOI: 10.1016/j.forsciint.2011.09.006</a>).
"This may seriously influence the interpretation of trace analysis
results taken during autopsies," says Nicole von Wurmb-Schwark who was
also involved in the work. For example, fragments of DNA from previous
autopsies could mask or <a href="http://www.newscientist.com/article/mg20727733.500-fallible-dna-evidence-can-mean-prison-or-freedom.html">confuse DNA profiles</a> from genuine assailants.</p>
<p class="infuse"><a href="http://www.med.uio.no/klinmed/english/people/aca/petergi/" target="nsarticle">Peter Gill</a>,
former principal scientist at the UK's Forensic Science Service, now at
Oslo University in Norway, says scientists should not dismiss the
possibility of contamination, particularly where tiny amounts of DNA are
concerned.</p>
<p class="infuse">"DNA is ubiquitous," he says. "There
are lots of examples where inadvertent transfer of DNA has happened. The
problem is these evidence items are often kept in plastic bags and if
you have got heavily bloodstained items, for example, then DNA is going
to transfer across items."</p>
<p class="infuse">That's not to say touch evidence
shouldn't be used to help solve crimes, but jurors need to be presented
with information about its limitations or wrongful convictions may
ensue, while other convictions may fail or be overturned on appeal.</p>
<p class="infuse">"I think that when we're dealing with
very low levels of DNA we need to report that a DNA profile matches, but
as to how and when it got there we just don't know," says Gill.<br clear="all"></p></div></div></div><br><br>-- <br>Art Deco (Wayne A. Fox)<br><a href="mailto:art.deco.studios@gmail.com" target="_blank">art.deco.studios@gmail.com</a><br>