This week, the boy's biological father, Brendan William Collins is wanted for arrest - though has been ruled out as a suspect in the case of the missing child.
Collins is wanted concerning a failure to appear in court, where he was being trialled for carrying stolen credit cards.
He was arrested on the charges in November last year, and noted to be "unsteady on his feet."
Collins' former partner, Karlie Tyrrell, is William Tyrrell's biological mother.
Last year, a bombshell court ruling revealed that William was indeed in foster care at the time of his disappearance.
He was therefore in the care of the Department of Family and Community Services (FACS), being cared for by his foster parents when he went missing from his foster grandmother's house.
Statutory restrictions previously prevented this from becoming public knowledge but a Supreme Judge has now deemed this information to be "legitimate public interest."
Last year an unprecedented award of $1 million was offered by the NSW government, for any information leading to the recovery of William Tyrrell.
In September last year, lead investigator into the disappearance of William Tyrrell said authorities had significantly narrowed down persons of interest surrounding the highly-publicised case.
Speaking with 9 News, Detective Chief Inspector Gary Jubelin of the NSW Police Homicide Squad said it was "highly likely" police had already come across the perpetrator of the crime.
Det. Jubelin added that police are now turning their attention to a group of just a few hundred persons of interest, narrowed down from a list of thousands.
"The strongest likelihood is that we've already got the name of the person involved," he said.
"I would be sweating."