Former detective Gary Jubelin has denied claims he threatened Bill Spedding in an unrecorded police interview at the time he was investigating the disappearance of three-year-old William Tyrrell.
Giving evidence in court on Wednesday, Mr Jubelin rejected suggestions he had threatened Mr Spedding after his arrest in April 2015 for historical sexual assault charges.
Barrister Adrian Canceri claimed Mr Jubelin said "Mr Nice Washing Machine Man, I am going to ruin you" during an interview in custody at a Port Macquarie police station.
Mr Jubelin denied he uttered those words.
"I've made no threats to Mr Spedding," he told Justice Ian Harrison in the NSW Supreme Court on Wednesday.
Suggestions Mr Jubelin had asked whether Mr Spedding knew how to dispose of a body were also roundly rejected by the detective.
Mr Spedding was a white goods salesman who became a high-profile person of interest in the disappearance of William in September 2014.
After a search of his Bonny Hills home in January 2015 failed to turn up any trace of the toddler, Mr Spedding was arrested over historical sexual assault allegations in April that year.
He is suing the state of NSW for malicious prosecution after being held in custody for 58 days until bail was granted in June 2015, and is seeking damages for false imprisonment and loss of reputation.
On Wednesday, Mr Jubelin admitted that after Mr Spedding had been arrested over the sexual assault, he was specifically questioned while in custody about William's disappearance.
"At that stage, you were targeting Mr Spedding, would you agree?" asked Mr Canceri.
"I would agree, yes," Mr Jubelin replied.
While frustrated at the time that the investigation was still ongoing seven months after William's disappearance, Mr Jubelin rejected claims this had made him threaten or intimidate Mr Spedding during the interview.
"I'm a professional detective. I'd been investigating homicides for almost 25 years at that stage. And this is pressure that I'm not unaccustomed to," he told the court.
Following bail, Mr Spedding says he suffered humiliation, embarrassment and the indignity of strict rules, which included not seeing his foster grandchildren.
He is claiming the legal fees paid defending himself as well as psychological counselling over four years since he was ruled out as a person of interest.
The trial continues.