The officer in charge of the Lundy double-murder case was told evidence held on slides had degenerated and should "remain a mystery", a court was told today.
However, the evidence was taken to Dallas, Texas in the United States and was tested by a pathologist.
Inspector Ross Grantham was cross-examined about his role in the murder investigation in the High Court at Wellington today.
Mark Lundy, 56, has denied killing his 38-year-old wife Christine and 7-year-old daughter Amber at their home in Palmerston North on August 30, 2000.
Mr Grantham told the court today he had secured samples of evidence in his safe at the Palmerston North police station before taking them to Texas.
The samples included slides with evidence from Lundy's polo shirt, which the Crown says has his wife's brain tissue smeared on it, as well as the shirt itself.
On January 9, Mr Grantham met with a neuropathologist Dr Heng Teoh who had looked at a slide of evidence.
"Dr Teoh said a man could not be convicted on the strength of one glass slide - they were too degenerative and should remain a mystery," Mr Grantham said under cross examination by defence lawyer Ross Burns.
On February 3, Mr Grantham said he took the evidence and travelled with the items to Texas for testing by pathologist Rodney Miller.
He told the court he was present while Dr Miller performed tests on the shirt.
Mr Burns asked what protective clothing they were wearing.
Mr Grantham said he wore gloves if he was touching the evidence and Dr Miller wore surgical scrubs and gloves.
Dr Miller was able to take 10 slides of evidence from the two marks on the shirt, plus 10 slides from a control sample, Mr Grantham said.
The trial in front of Justice Simon France and a jury of five women and seven men continues.