Speaking from his office in Dallas, Texas via audio-visual link Dr Miller told the jury in the High Court at Wellington there was no way the shirt was contaminated by anything in his laboratory.
"The tissue was mashed into the shirt fibres, if it was picked up as a contaminant it would likely have fallen off and that is something we rarely see."
The Crown's case is that stains on Lundy's shirt were brain matter from his 38-year-old wife, Christine.
Lundy, 56, has denied killing her and their 7-year-old daughter Amber in their Palmerston North home on August 30, 2000.
Dr Miller was given samples of the stains on slides as well as the shirt by the officer in charge of the case, Inspector Ross Grantham, in February 2001.
Mr Hislop asked Dr Miller what Mr Grantham was wearing when he helped with some of the testing.
Dr Miller said Mr Grantham wore gloves at the time but not a lab coat as there would have been no reason for him to wear one.
"How on earth do you know what was on his clothes?" Mr Hislop asked.
"Oh please, how do you get brain tissue on you by eating a sandwich?" Dr Miller replied.
He said benches used when working on Lundy's top were free from debris and were "obviously clean".
"The type of contamination that you are trying to allege just doesn't happen, and I can tell you that because I've been doing this for 30 years."
He also told the court that in January last year he recreated the circumstances of Lundy's shirt, with his own - known as the Miller shirt.
He smeared the top with fresh brain tissue and then stored it in a paper envelope in his office.
After 28 days he tested part of the shirt and said the results showed "exactly what you would expect to see with brain".
"The results of the Miller shirt were identical [to the Lundy shirt]," Dr Miller said.
The same tests were undertaken on pieces of the shirt after 95, 159 and 365 days of the shirt being stored in Dr Miller's office.
The results were the same with no "significant degradation or degeneration" of the tissue, he said.
The jury was also shown the stain from Lundy's shirt that was magnified 1000 times.
"You can see a tangled network of neurofilament structures," Dr Miller said.
He defended his technique and told the court the process he used was "highly controlled and fundamentally sound".
"I go the extra mile to make sure my immuno stains are correct."
The process had been "standard practice" in pathology for years, Dr Miller said.
The trial in front of Justice Simon France continues.
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