UPDATED 4.23pm: A Dutch forensic scientist says it's probable a stain found on Mark Lundy's polo shirt, contained human brain tissue.

Dr Laetitia Sijen has taken the stand in Lundy's retrial for the murders of his wife and child.

Lundy's on trial for the August 2000 murders of Christine and Amber Lundy, in the High Court in Wellington.

Dr Sijen is an expert in human biological traces at the Netherlands Forensic Institute.

She's outlined for jurors complicated tests carried out on samples taken from the sleeve of the shirt, using domestic animal brain tissue as a comparison.

"From these results we infer that its more probably that human CNS (central nervous system) tissue is present, than tissue of the other animals we tested."

Dr Laetitia Sijen says the stain on the pocket of the shirt didn't have signs of brain tissue, but it could still be present.

The tests were carried out in front of an expert Lundy's defence team will call as a witness.

Earlier today the court heard from British forensic expert Gillian Leak, a defence witness who was called early.

She told the High Court in Wellington the way police examined evidence found in Mark Lundy's car, was 'unusual'.

Lundy's defence lawyer David Hislop, QC, asked about police taking a black suit that had a polo shirt inside out of Lundy's car, and then returned.

Mrs Leak says that creates a contamination risk, and that it's unusual to take the bag out of the car.

"It's unusual to take it out, so by nature that will be unusual to put it back."

While under cross examination from Crown prosecutor Philip Morgan, the jury heard from Gillian Leak it's likely Christine Lundy was asleep, when the fatal attack was carried out.

Mr Morgan referenced a report Mrs Leak had put together for the trial - in which she says came to the conclusion for a number of reasons, including the fact the television was in standby mode, Mrs Lundy had taken her glasses of, and the assailant managed to get next to the bed before the attack began.

This morning jurors were told smears of blood on the window frame of the Lundy home could've been put there by those investigating the murder scene.

Leak says she can't rule out the possibility investigators put the blood there, as they were getting changed out of scene suits near the partially open window.

"When you're trying to take a scene suit off at a scene you're invariably balancing as you try and take those layers off over what you're already wearing underneath," she says. 

"It might be that you've leant against something to stop yourself falling over."

Leak agreed with Philip Morgan that the blood stains could've also been put there by a gloved hand that had Christine Lundy's blood on it, saying it was one explanation.