The inquest into the disappearance of William Tyrrell is set to begin today in Sydney almost five years after he went missing.

The NSW coroner will examine the toddler's family situation and the initial response to his disappearance.

William vanished from his foster grandmother's home on the NSW mid north coast on September 12 2014 while wearing a now infamous Spiderman costume.

Police have worked tirelessly to track down the missing child but there has been no trace of him.

William Tyrrell disappeared from Kendall, New South Wales 12 September 2014. Photo / File
William Tyrrell disappeared from Kendall, New South Wales 12 September 2014. Photo / File

A massive brief of evidence, containing at least 15,000 items, will go before Deputy State Coroner Harriet Grahame at the launch of the inquest this morning.

But, according to The Sun Herald and the Sunday Age, the inquest will focus on a new person of interest — a man who has never been publicly discussed by detectives.

Throughout the investigation, William was referred to "a little boy lost" but police soon came to suspect something more sinister happened and zeroed in on known paedophiles and criminals from nearby holiday towns.

But no one has been charged for the suspected abduction.

AAP understands investigators hope the first week of hearings will show William did not wander into nearby bushland but was, instead, snatched by a predator.

In mid-2018 they conducted a large-scale search of bushland near the Kendall home to rule out misadventure and firm up their theory.

The closely-guarded persons of interest list, which ballooned to include hundreds of names over the years, has been whittled down for the inquest's second sitting in August.

Some names on that list have been previously released by police but sources say one so-far unidentified person will be watched closely when they are called in front of the inquest.