Suspects in the disappearance of William Tyrrell will be hauled before a public probe, almost five years after he was most likely snatched from his foster grandmother’s backyard.

The NSW coroner has been hearing evidence to determine what happened to William, who was aged three years and three months when he vanished at Kendall on the state’s mid north coast on September 12, 2014.

William’s biological and foster parents have given evidence in the first week of the inquest, described as the “tip of the iceberg” by senior counsel assisting the coroner Gerard Craddock SC and Deputy State Coroner Harriet Grahame.

William was last seen playing in the backyard of his foster grandparents’ home.

Persons of interest will have to front the public inquiry and give evidence in August.

The biological parents, who can’t be identified and are no longer in a relationship, were the final witnesses to give evidence on Thursday.

The father admitted he hid William from authorities for weeks when he was a baby, but denies he played a part in his disappearance.

He said authorities, including the Department of Family and Community Services, had “f-–ed up”.

“It was the minister’s duty of care to keep him safe until he was 18 and that was not the case at all. FACS was about keeping kids safe.”

Both parents conceded they “absconded” with William for five to six weeks in early 2012 after a children’s court ordered he be placed in foster care.

“I couldn’t bring myself to give them my son,” the mother told the NSW Coroners Court.

The father said he was upset, annoyed and angry.

“I was the No.1 person not letting him go. The No.1 person putting that [idea] forward,” he said.

The mother said she first found out William was missing hours later when police knocked on their door in Sydney.

“They didn’t tell me anything. They asked me if William was there. They looked around, they thought [my other] son was William – he wasn’t. They asked what I’d done … and left.”

The mother told the court she was aware of adoption plans before William disappeared but not in any detail and “didn’t agree” with them.

“We were still trying to get the children back. We were at court,” she said.

Police search dense bushland for evidence of the missing William Tyrrell. Photo: AAP

William’s foster father, who gave evidence on Wednesday, said he was in Kendall and had driven to nearby Lakewood about 9am to find a strong internet connection for a conference call.

He sent a text to his wife about 10.30am saying he’d be home in the next five minutes, when he returned home and his wife asked: “Is William with you?”

“Why would he be with me?” he replied.

The foster mother called police at 10.56am to report the boy missing, estimating he’d been gone since 10.30am.

Mr Craddock on Wednesday asked why the foster father didn’t stop and talk to his wife about where she’d searched before he sprung into action.

“I had assumed in the time that I got home, if she couldn’t find him, that she’d already actually done the immediate area, including inside and outside the house,” the man said.

He looked under houses, external fences, pits, drains and sheds.

“Everything, everywhere he might have gone,” he said.

The foster father joined the extensive police and State Emergency Service search for four days after William’s disappearance on the Friday morning.

Come nightfall, he began to worry about food and shelter for William, “if he was lost”.

When asked by Mr Craddock if he believed William would be found over the weekend, the foster father replied: “I had hope. I had hope.”

William’s foster mother has previously testified her immediate thought when the boy fell silent while playing around the home was that he’d been snatched.

Mr Craddock said the police investigation continues.

A directions hearing will be held on April 24 before four weeks of hearings in August, when the persons of interest will be called to give evidence.

-with AAP