The lead investigator into Lynette Dawson’s disappearance has said he was concerned about journalist Hedley Thomas contaminating evidence through his podcast, The Teacher’s Pet.

Detective Senior Constable Daniel Poole returned to the NSW Supreme Court on Wednesday to give evidence in Christopher Michael Dawson’s murder trial. 

The police officer said concerns had been raised about how witnesses’ recollection of events around Mrs Dawson’s disappearance four decades ago could be negatively impacted by either listening to The Teacher’s Pet podcast or speaking with Thomas.

He agreed with statements from Dawson’s barrister Pauline David that care had to be taken to ensure witnesses were impartial when giving statements to the police.

Thomas’ approach to interviews was inappropriate because he had told some potential witnesses what others had said. This, along with simply listening to the podcast, could lead to unconscious contamination, Justice Ian Harrison heard.

“The difficulty with unconscious contamination is that the person believes what they are saying is accurate and doesn’t recognise the manner in which they are influenced,” Ms David said.

“Yes,” Det Poole agreed.

The police were then cautious with the reliability of witnesses who had appeared on or listened to The Teacher’s Pet, the court heard.

Crown prosecutor Craig Everson SC told the court that although some witnesses called in the long-running trial had made police statements after they spoke to Thomas, the majority had talked with police and given evidence at coronial inquests over a decade before speaking to the journalist.

“They’d already said what they had to say long before Mr Thomas spoke with them,” he said.

Det Poole admitted using The Teacher’s Pet to the police’s advantage, tapping the Dawson family phones to see if any conversations were stirred up as a result of the podcast. However, he stressed this was not done in cooperation with Thomas.

Dawson, now 73, is accused of murdering his wife and disposing of her body in January 1982 so he could have an unfettered relationship with one of his former high school students, known as JC, while holding onto assets such as the family home in Bayview, Sydney.

He has pleaded not guilty to the charge and denies any involvement in Mrs Dawson’s disappearance.

The trial continues.