The defence in Chris Dawson's murder trial says a detective investigating the case was "incapable" of considering any evidence that did not support the theory their client murdered his first wife.
Mr Dawson is charged with killing Lynette in January 1982 in order to pursue an "unfettered relationship" with the family's 16-year-old babysitter, known as JC, who was also a student at the high school where he taught.
He denies any involvement in Ms Dawson's disappearance.
Today, the court heard that when Damian Loone took over the investigation of Ms Dawson's disappearance in 1998, he had been handed a missing persons report and been told to "put the case before the coroner".
He said that at the time, he and officers in his unit had discussions about whether "something sinister" had happened to her.
"You formed a view at that early stage, just simply based on that piece of paper and what the other officers in your unit had told you, that something sinister had happened," defence barrister Pauline David asserted.
"Yes," Mr Loone replied.
"And you set out on a path to prove that Chris Dawson was the man who did something sinister," she went on.
"Yes," he said.
He agreed that by the time he conducted his first interview with JC, he had formed a view Mr Dawson had killed Ms Dawson.
When asked whether he thought JC may also have had a motive, he said that as far as he was concerned "there was no motive on her behalf".
"Her answers appeared to be truthful," he told the court.
Ms David also questioned Mr Loone over his interactions with Mr Dawson's friend, Philip Day, who claimed to have been with the accused man at Northbridge Baths on Sydney's northern beaches on January 9, 1982, the day after Ms Dawson disappeared.
She asked him why, despite meeting with Mr Day twice and making detailed notes, he never took a formal statement.
"You were not interested in taking a statement from Philip Day, were you?" Ms David pressed.
"You were entirely uninterested in what he had to say."
Mr Loone conceded that in 2001 he may have failed to get back to another witness who made contact with police — a woman who claimed had been working at the Baths on that day.
"You didn't want to do anything that would corroborate Chris Dawson," Ms David said.
Mr Loone agreed that none of the alleged sightings of Ms Dawson in the time after her disappearance, including one at the Rockcastle Hospital in 1984, were handed up to the coroner ahead of the 2001 inquest into her disappearance.
Mr Loone said inquiries had revealed Ms Dawson had never worked at the hospital.
"She wasn't employed there ... she wasn't a registered nurse at the time," he said.
"We would have made diligent inquiries ... those sightings were not confirmed."
The trial, before Justice Ian Harrison, continues.
