William was just three years old when he went missing from his foster grandmother's home in Kendall, NSW, in September 2004.
The toddler was reportedly playing in the yard when he went missing.
At the time of the disappearance, an extensive 10-day search involving police, locals and emergency services was conducted, but William was never found.
On the second anniversary of William’s disappearance in 2016, the NSW government announced a $1 million reward for information leading to his recovery.
Detective Chief Inspector Gary Jubelin told reporters: 'We’re committed to finding out what’s happened to William.
'We’re mindful that it’s over three-and-a-half years since William disappeared and we haven’t solved the matter. We will continue on until we do solve this matter.
'I think based on what took place during the original search and from our investigations it’s reasonable to draw the conclusion that William’s disappearance as a result of human intervention and not through misadventure.
'The search we’re conducting now and fairly extensive search is so we can produce that evidence whether it be a coroner’s court or criminal court showing that William’s disappearance is a result of human intervention and not through misadventure.'
Detective Jubelin added that law enforcement have 'grave concerns' over William's whereabouts.
'It’s been a very long time,' he said. 'As I have said to the family and I can’t be any more honest than what I say to the family in a situation like this: until we know conclusively that William is not alive we will treat it with the possibility that he is still alive. Obviously we still have grave concerns.'
It is understood that NSW police are not expecting a breakthrough in the case, but were 'looking for evidence for court.'
New Idea Investigates
On Wednesday 10 February 1993 Wayne Crossingham, 34, refereed a game of touch football at Woodward Park in Liverpool, NSW.
He walked home that night - but as he made his way up the stairs of his apartment block he was brutally murdered. His killer has never been found.
In this episode of New Idea Investigates, we talk to Wayne's mum about that fateful night, and what happened next...