A pathologist told a jury yesterday that he would not attempt to fix the time that Joanne McCarthy was killed - one of the crucial issues in the Travis Burns murder trial.
The stance of Associate Professor Timothy Koelmeyer, called as a witness for the defence, runs counter to the opinion of a crown witness.
Burns, aged 32, of Titirangi, is accused of murdering the 33-year-old at her home in Whangaparaoa on November 12, 1998.
Earlier in the trial another pathologist, Dr Jane Vuletic, told the jury in the High Court at Auckland that she believed death occurred in the earlier part of the two-hour period between Joanne McCarthy last being seen alive at 11.35 am and being found dead around 1.40 pm.
But Professor Koelmeyer, a colleague of Dr Vuletic who said he had conducted more than 100 autopsies in homicide cases, said that fixing the time of death was merely a guess.
His practice over more than 20 years was "not to give the time of death."
"You could be hopelessly wrong."
Quoting a famous English pathologist, Professor Koelmeyer said the only thing that could be said was that death occurred between the time the deceased was last seen alive and when he or she was found dead.
There were so many variables that the result would be guesswork.
"And in a grievous matter such as homicide I don't guess.
"As far as I am concerned, and where my practice is concerned, in the matter of homicide I have not and will not attempt to give the time of death."
Crown counsel Christine Gordon said other eminent pathologists were prepared to estimate the time of death. Professor Koelmeyer replied that they were free to do so but he would not.
According to the Crown, Joanne McCarthy was killed between 11.35 am and 12.30 pm.
Burns was seen on a BNZ bank security video in Milford 30km away at 12.50 pm.
Earlier, evidence was given by a bank teller at the St Heliers BNZ, which Burns said he tried to rob four days after the killing.
Christine Chittenden said she was approached by a heavily bandaged man wearing a sling who she thought had been in a serious accident.
He handed her a bag and asked her to fill it with money.
"I thought, 'He hasn't got a gun or anything in the sling,' and I just said, 'No,' and shut the drawer, and with that he turned and walked out."
The Crown contends that Burns carried out the attempted robbery as a way to explain why he had bought a first-aid kit on the day of the killing.
According to the Crown, Burns bought the bandages to treat a wound inflicted by Joanne McCarthy.
Evidence has been given by the Institute of Environmental Science and Research (ESR) that material found under Joanne McCarthy's fingernails was 300 billion times more likely to be from Burns than from any other man in the country.
However, defence lawyer Barry Hart claims that there was cross-contamination of the samples at the ESR.
Yesterday, the defence called DNA expert Dr Arie Geursen, who gave evidence of contamination at the ESR to a ministerial inquiry last year.
"Scientists are like any human beings and errors can occur," he said.
Dr Geursen explained how cross-contamination could occur.
It would be prudent for murder scene samples and suspect samples not to be analysed at the same time or in the same laboratory, he said.
Evidence was given earlier in the trial that no DNA was in fact found on the suspect sample-a piece of carpet taken from Burns' car.
But Mr Hart contends that only a small part of the carpet was tested.
Burns' DNA, he suggested, might have been on another part of the carpet and made its way into the fingernail samples from the dead woman during testing.
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