No forensic evidence, no known eyewitnesses and a "sneaky, complex" abductor make the disappearance of William Tyrrell among the world's hardest cases to solve, an inquest has been told.
Dressed in a Spider-Man outfit, the three-year-old vanished while playing in the garden of his foster grandmother's home in Kendall on September 12, 2014.
Despite hundreds of claimed sightings, intense searches of nearby bush and dozens of interviews, police still have no fixed conclusions on where William went, counsel assisting the coroner Gerald Craddock SC told the NSW Coroners Court on Wednesday, August 7.
This second round of evidence in the coronial inquest into the boy's disappearance is underway.
Mr Craddock said 97 per cent of child abductions in the United States involved family members or close acquaintances but a stranger could have taken the boy.
"The present state of evidence is if William was murdered - and that's a big if - it may be one of those rare, three per cent of cases," Mr Craddock told the inquest.
The offender is a sneaky, complex offender who has hidden their desires for some time and has chosen to act on those desires.Counsel assisting the coroner Gerald Craddock SC
"(For cases with no eyewitnesses and no evidence) worldwide, these cases have proven the most difficult to solve."
Mr Craddock said William was likely taken by car and police remained of the belief they could solve the case.
"The offender is a sneaky, complex offender who has hidden their desires for some time and has chosen to act on those desires."
On August 19, the inquest is set to move to Taree, and focus on the police investigation to find William.
In 2018, during a fresh investigation of the case, police intensely searched more than 40 hectares of bush immediately surrounding the foster grandmother's home.
The inquest was told toys, backpacks, shovels, animal bones and a speargun were among the items uncovered - but none were deemed to be related to three-year-old's mysterious disappearance.
Mr Craddock said people treated the forest as a convenient place to dump all manner of things.
Detective Sergeant Laura Beacroft, who helped organise a new land search in 2018, said she understood that was the first time police were looking for evidence of deliberate human intervention and not just signs of misadventure.
"My understanding was it was a new notion," she said.
Another police officer involved in the search, Senior Constable Daniel Dring, agreed no stone was left unturned in the search area during the 20-day search by dozens of police and other emergency services personnel.
"I trust the team and I trust the method and I am extremely confident William was not in the area," Snr Const Dring told the inquest.
This is an inquest and not a criminal trial.Counsel assisting the coroner Gerald Craddock SC
Jailed people and police detectives would be among about 54 witnesses to give evidence during the hearings in Sydney and Taree until August 30, Mr Craddock said.
He stressed any suggestion that those called to give evidence were suspects was "simply wrong".
"This is an inquest and not a criminal trial," he said.
"There has not yet been a conclusive breakthrough (in the police investigation), otherwise someone would have been charged and we wouldn't be here."
Former detective inspector Gary Jubelin, who led the fresh investigation into William's disappearance, was among those to attend the inquest on Wednesday.
He has pleaded not guilty to four charges of illegally recording conversations while leading the investigation in late 2017 and 2018.
The inquest continues.