The absence of eyewitnesses and forensic evidence makes the investigation into William Tyrrell's suspected abduction among the hardest cases in the world to solve, a Sydney inquest has been told.
The coronial inquest into the disappearance of the child from Kendall in September has resumed a second round of hearings at the NSW Coroner's Court today (August 7).
The first round of hearings commenced in March this year and heard evidence from William's biological and foster parents, as well as emergency services personnel who were on the ground in the first moments after he vanished from his foster grandmother's front yard in Benaroon Drive.
The inquest was told police have no fixed conclusions about what happened to the boy.
Police remain hopeful they can solve the case but there are no eyewitnesses and no forensic evidence, counsel assisting the coroner Gerard Craddock SC said.
Mr Craddock said people called to give evidence will simply help put the pieces of the puzzle together and are not on trial.
All of the evidence collected by Strike Force Rosann is being presented before Deputy State Coroner Harriet Grahame who will determine if the three-year-old did succumbed to the rugged bushland around his grandmother's home, or was abducted by someone. There is evidence yet to conclude that William is dead.
Newly appointed officer-in-charge of the investigation Detective Chief Inspector David Laidlaw - stepping into the role after the resignation of Detective Chief Inspector Gary Jubelin earlier this year over allegations of misconduct - is expected to give evidence.
"Worldwide, these cases have proven the most difficult to solve," Mr Craddock said in his opening address.
He stressed any suggestion that those called to give evidence were suspects is "simply wrong".
"This is an inquest and not a criminal trial," he said.
The coronial inquest will sit for two weeks before travelling to the Taree Courthouse on August 19 where theories about what may have happened and who may have been involved will be examined.
A $1 million reward remains in place for information leading to the return or recovery of William Tyrrell. It is one of the largest rewards offered in NSW history.