Lloyd Rayney's defence yesterday continued to attack the integrity of the police handling of two liquidambar seed pods taken from the hair of his murdered wife Corryn.
To questions, forensics officer Sen. Const. Scott Walker agreed it appeared a bag the pods were in may not have been properly sealed against contamination.
He also had difficulty explaining to Mr Rayney's wilful murder trial why he believed so strongly that he broke an official seal on the bag when showing the pods to scientists, despite a photo showing the first time it was sealed was after this examination.
Sen. Const Walker's recollection of events at the WA Herbarium on August 20, 2007 came as defence lawyer David Edwardson continued questioning police handling of the two pods.
The Supreme Court has been told the two spiky one-inch pods were found during an autopsy on August 17, 2007 - 10 days after Mrs Rayney's estranged husband allegedly killed her and the day after she was exhumed from a bush grave in Kings Park.
The prosecution claims the pods became tangled in Mrs Rayney's hair as her body was dragged outside the couple's Como home where there is a liquidambar tree. It claims soil particles in one pod matched soil in the yard.
The defence this week challenged evidence about how the pods were found, noting no photos were taken of them "in situ" in her hair.
Mr Edwardson asked Sen. Const. Walker whether the pods' exhibit bag was sealed properly with evidence tape.
The officer said he was sure that, in line with his statement and running sheet, he broke an existing seal when he showed the pods to botanical experts and applied a new seal afterwards bearing the date and his name.
A photo taken later of the bag shows the earliest seal was the one he applied that day.
Sen. Const Walker agreed it looked as if the bag was not sealed before he took it to the scientists but said there might have been another sealed container inside the bag. The bag was still being located yesterday.
Sen. Const. Deborah Freegard testified she was present when hair and debris samples were later taken from the pods.
She took photos of the exhibit bag before it was opened, of the pods next to new containers of extra samples and of the bag re-sealed with the pods back inside.
She could not remember whether the pods had been inside another container in the bag.