Mix-up in DNA test doubtful: scientist

An ESR scientist repeatedly cross-examined this week about contamination of DNA samples said again yesterday, it was unlikely to have occurred in the Travis Burns murder case.

Dr Sally-Ann Harbison had been questioned in the High Court at Auckland by Burns' defence team after telling the jury that DNA evidence found on the fingernails of victim Joanne McCarthy was millions of times more likely to have come from the accused than any other man in the country.

Ms McCarthy was killed in her Whangaparaoa home in November 1998.

During re-examination yesterday, Crown Solicitor Simon Moore asked Dr Harbison about defence lawyer Barry Hart's theory that the evidence could have been contaminated at the Institute of Environmental Science and Research (ESR) by Burns' DNA on his car carpets.

"I think it unlikely that a small flake from any of the samples [of the carpets] could have found its way into the sample [of the fingernail]," she said.

"But even if it had occurred I think it's extremely unlikely it would have been possible to obtain a DNA profile of any type from such a small, introduced piece of that particular carpet."

Dr Harbison admitted during her week in the witness box that one sample from Ms McCarthy had become contaminated with her own DNA, possibly by her coughing over it.

She denied yesterday making an attempt to cover it up.

Mr Hart had also asked her about an ESR mistake when DNA from a man who was badly beaten in Christchurch ended up in samples from two Wellington homicides.

Although she refused to rule out any option, Dr Harbison agreed with reports into the incidents that accidental contamination at the ESR was the most likely explanation.

She said the usual protocol followed by staff was not to analyse different samples in the same area at the same time.

The trial before Justice Chambers will resume on Monday.