[Vision2020] How DNA contamination can affect court cases

[Art Deco]

 My New Scientist

Just think of the possibilities when currency is handled by many people.


________________________________________________
 How DNA contamination can affect court cases

   - 13 January 2012 by *Linda
Geddes*<http://www.newscientist.com/search?rbauthors=Linda+Geddes>
   - Magazine issue 2847 <http://www.newscientist.com/issue/2847>. *Subscribe
   and save* <http://subscribe.newscientist.com/bundles.aspx>
   - For similar stories, visit the *Crime and
Forensics*<http://www.newscientist.com/topic/crime-and-forensics>Topic
Guide

   [image: Handle with care <i>(Image: Anthony Devlin/PA Wire/Press
Association)</i>]

Handle with care *(Image: Anthony Devlin/PA Wire/Press Association)*

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.

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.

Although there was additional evidence against Dobson and Norris that
helped to secure their conviction, several new studies illustrate that
contamination<http://www.newscientist.com/article/dn18215-knox-murder-trial-evidence-flawed-say-dna-experts.html>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.

"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 Forensic
Institute<http://www.theforensicinstitute.com/>in Glasgow, UK. "The
finding of someone's DNA implies their presence. But
presence is not a necessary consequence of finding someone's DNA."

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 (*Legal Medicine*, DOI:
10.1016/j.legalmed.2011.09.006<http://dx.doi.org/10.1016/j.legalmed.2011.09.006>
).

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 (*Forensic Science International Genetics*, DOI:
10.1016/j.fsigen.2011.03.013<http://www.sciencedirect.com/science/article/pii/S1872497311000810>).
"There is a distinct possibility for the misinterpretation of a result that
could impact negatively on the criminal investigation," says Goray.

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 (*Forensic Science International*, DOI:
10.1016/j.forsciint.2011.09.006<http://dx.doi.org/10.1016/j.forsciint.2011.09.006>).
"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 confuse DNA
profiles<http://www.newscientist.com/article/mg20727733.500-fallible-dna-evidence-can-mean-prison-or-freedom.html>from
genuine assailants.

Peter Gill <http://www.med.uio.no/klinmed/english/people/aca/petergi/>,
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.

"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."

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.

"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.


-- 
Art Deco (Wayne A. Fox)
art.deco.studios at gmail.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.fsr.com/pipermail/vision2020/attachments/20120123/7c93d494/attachment-0001.html>