The three-year-old went missing while playing on the verandah at his foster grandmother's home in Kendall, on the NSW mid-north coast, on September 12, 2014.
The inquest examining what happened to the toddler reopened on Monday.
Counsel assisting Gerard Craddock SC said the focus would be on a police search in 2021 as well as a theory that William died in an accident on the property and that his foster mother disposed of his body.
Mr Craddock said the alleged motive was that the woman and her husband would lose custody of another child under their care if the death was uncovered.
The foster mother denies having anything to do with William's disappearance.
Mr Craddock told the court that police searches, which were "intensive, thorough," had failed to turn up any forensic evidence into the fate of the three-year-old.
On Tuesday, coroner Harriet Grahame will continue to hear evidence about the 2021 search for the toddler's body.Â
Senior Constable Jost Preis will discuss the methodology of the search, including the use of GPS trackers to ensure that every patch of ground was covered.
Forensic anthropologist Dr Jennifer Menzies will then take the stand to discuss the decomposition of a body and how bones are broken down or preserved in certain environmental conditions.
If time allows, additional evidence about efforts of police to identify those in the area when William disappeared as well as the use of both search and cadaver dogs to locate him will also be heard.
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