Police will never give up on William Tyrrell investigation, inquest told

Counsel assisting the inquest Gerard Craddock, SC, asked Mr Laidlaw at the outset of his evidence: "Have you given up?"

"No," Mr Laidlaw said. "We never will."

Mr Laidlaw said active investigations were continuing in the case and police were due to go back into the field later this year. He declined to elaborate because "investigations are ongoing".

The police officer said that, when he took over the investigation, he decided not to get a handover or debriefing from Mr Jubelin.

He said instead, he spoke to "every one" of the investigators on Strike Force Rosann, the homicide squad team investigating William's disappearance.

"My view at that stage was I was going to get more knowledge of the investigation from all those who worked on it, not just one person," Mr Laidlaw said. "It’s always been with me, it’s 'we rather than me'."

Earlier on Wednesday, a memory expert told the inquest that a reported sighting of William in the back of a speeding four-wheel-drive on the day of his disappearance could have been that of a different child, or could have been William on an earlier day.

Ronald Chapman previously told the inquest he was at the front of his home on Laurel Street, near Benaroon Drive where William disappeared, about 10.45am on September 12 when he saw a woman speeding past with an unrestrained boy dressed in a Spider-Man suit in the back of her car.

"I definitely saw William. I'm 100 per cent sure it was William in the back of the car. No doubt," Mr Chapman said.

Dr Helen Paterson, a senior lecturer in forensic psychology at the University of Sydney, outlined research and literature on memory creation and retrieval and explained how memory operates, including how witness perception of an incident can be influenced by "post-event information" such as watching a news report.

Dr Paterson said Mr Chapman "originally wasn't very confident at all" about what he had seen and "wasn't sure if it was a dream", but became more confident over time that he had seen William.

She said it could be the case that Mr Chapman "saw a car go by with a child in it that was unrestrained" and later watched the news and incorporated William into his memory, or that he did see William on a completely different day and misremembered that he saw the speeding car on the day William went missing.

Dr Paterson was also asked about the memories of William's foster mother, particularly the memory of two parked cars she saw on Benaroon Drive on the morning William disappeared.

The foster mother said the memory of the cars was "burnt in my brain".

Dr Paterson said she could not say if the memory of the cars was genuine or false, but could say it was "a possible false memory".

"There was a leading question at one stage - 'There weren’t any suspicious vehicles were there?' - that may have implanted in her mind … 'Were there suspicious vehicles?' " Dr Paterson said.

She said it is possible the foster mother did see the cars in that location at a different time and mistakenly believes they were there on the morning William disappeared.

The inquest continues.