DNA testing carried out on Jane's intimate swabs in 1996, 2001 and 2017 detected no male or female DNA.

Ms Barbagallo is now taking Mr Egan through when Jane's hair mass and its bucket arrived at the Pathwest lab, as well as branches taken from near her body.

The branch, known as RH21, was in 2017 found to have been contaminated with the DNA of the victim of an unrelated crime, whose exhibits were examined in the lab in the days either side of the branch testing in 2002.

Mr Egan said the unrelated case exhibit was examined on 31/1/02 in the examination area of the Pathwest lab.

On 4/2/02 in the same area, the examination of the RH21 branch occurred.

"Since that incident, we concluded that it appears a sample that was from a completely different case was examined around the same time as that branch," Mr Egan said.

"And that sample from the unrelated case was examined prior to the twig sample ... so probably some consumables or tubes were contaminated ... and that consumable has then been used as part of the examination of the twig sample.

"[The examinations] were three working days apart, there was a weekend in the middle there.

"One employee did the unrelated case and another employee did the twig."

Mr Egan said the investigation concluded the contamination most likely occurred in the DNA lab, on a tube batch used in the testing of both cases.

"There might have been an operator error where a bit of the DNA from the unrelated case was in the tube [used for RH21]," he said.

The DNA run was recorded at the time as a "lab error" and no results were recorded for any items tested.

Mr Egan said the contamination was a one-off in the Macro exhibits, but was not detected when the DNA testing results came through in March 2003.

The error was only detected in 2007 when another person reviewed the result.

"A review of the results identified a profile and that profile was looked at because it didn't match the profile of the girls in the case, so because it was a different profile, an investigation was done," Mr Egan said.

The type of contamination is known as secondary transfer, where DNA is transferred from one thing to another through an intermediate such as a piece of laboratory equipment.

This is the type of contamination defence lawyer Paul Yovich said is most likely to have occurred with Mr Edwards' DNA making its way into Ciara's fingernail exhibit.

The closest timeframe the items were tested to each other was two weeks.