• Claimed that scientists did ' />

Key evidence:
• Evidence given to the court last week showing brain matter on Lundy's top has been criticised
• Claimed that scientists did not follow written instructions on the testing process
• The test used in identifying RNA could give variables
• Degraded RNA would not give reliable results

The method used by an international scientist to show brain matter on stains on Mark Lundy's polo top was flawed, a court was told today.

Professor of molecular medicine Stephen Buston, from Angela Ruskin University in Cambridge, UK, gave evidence for the defence in the Lundy double-murder trial in the High Court in Wellington.

He has been challenging evidence by prosecution witness, Laetitia Sijen of the Netherlands Forensic Institute, who found tissue from a brain on the shirt, which the Crown said was likely to have come from Lundy's wife Christine.

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Lundy, 56, has denied killing her and their 7-year-old daughter Amber, who were found dead in their Palmerston North home on August 30, 2000.

Dr Sijen from the Netherlands Forensic Institute told the court last week she arrived at her conclusion that brain matter was present on the shirt based on tests performed on RNA in the sample.

RNA indicates which part of the body cells came from -- different to DNA which would indicate who the cells belonged to.

Prof Buston told the jury Dr Sijen did not follow written instructions when conducting tests on the sample.

"When you bake a cake you should follow instructions. But if you don't follow instructions, you should explain why you are not following the instructions."

There were problems with timings and the test, he said. The instructions said the testing time should be for 90 seconds, rather than 30 seconds used in Dr Sijen's test.

She also used less "primer" to detect RNA then the instructions specified, Prof Buston said.

"The method they are using for the detection of RNA is not really fit for purpose.

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"I would be highly reluctant to accept the results of the [tests] because of the technique that has been applied."

Prof Buston also pointed to the process the institute used to test the RNA, Reverse Transcription, which gave variables, but it was the only test available to use.

He was also surprised to see that tests were performed on the RNA years after the tissue was deposited on the shirt because he did not realise the RNA would last for so long.

He had since discovered it was possible, but great care was needed to be taken with the samples, including how they were stored.

If the RNA was degraded, results might not be reliable, he said.

The trial in front of Justice Simon France continues.