EXPLAINED: How victim’s DNA got into accused’s underpants
THE Crown case into the 2010 death in custody of Grafton Jail inmate Ian Klum concluded with evidence from a DNA expert.
The Supreme Court jury in the trial of Mr Klum's cellmate Shane Leslie Johnson, charged with the murder of Mr Klum, heard evidence that Mr Klum's DNA had been found in Mr Johnson's underpants worn at the time of an alleged altercation which is claimed to have caused the brain injury that killed him.
Yesterday, DNA expert Clayton Walton, from the NSW Health Forensic and Analytical science Service, returned to the witness box to conclude his evidence in chief.
He concluded that DNA discovered in the front of underpants was 850 times more likely to come from Mr Klum than a member of the general population. He said the major sample collected from the underpants belonged to Mr Johnson, but a minor sample was likely to come from Mr Klum.
Defence barrister Mr Watts cross examined Mr Walton's evidence about the DNA in the underpants and other samples collected from fingernails of the deceased and from a broken pair of glasses for most of the day.
He asked Mr Walton to explain the concept of secondary transfer of DNA.
Mr Walton said compared to primary transfer, where a person made contact with another person, leaving traces of their DNA, a secondary transfer occurred when another intermediary picked up a person's DNA and transferred it to a third person or object.
Mr Watts said this process could take place if Mr Johnson's hand had touch clothing or skin of Mr Klum or other surfaces in their shared jail cell.
When urinating he would have transferred DNA to his penis, which then would have come into contact with his underpants, explaining the presence of Mr Klum's DNA in the front of that garment.
Mr Walton agreed it was possible. But his answers to similar questions also introduced the principle of dilution, where each transfer of DNA reduced the number of cells in the sample.
Mr Watts compared the certainty of DNA sample in the underpants to a complete sample collected from Mr Klum's spectacles, which offered probability of 10 billion to one it was his DNA.
Mr Watts also asked Mr Walton to explain the findings from DNA collected from two of Mr Klum's fingernails.
The expert said there were traces of both men's DNA on them as well as the likelihood of DNA from one or more other people.
After cross examination, the Crown asked for clarification of some points from Mr Walton. The accused will begin his case today in front of Justice Geoffrey Bellew.