A "creepy" sex offender remained completely silent when he was interviewed by police about the disappearance and suspected murder of William Tyrrell, a NSW inquest has heard.

Robert Donohoe was working in a number of jobs, including as a volunteer with the SES and a casual in a nearby petrol station, when the three-year-old went missing in late 2014.

William had been playing in the yard of his foster grandmother's house in Kendall, on the NSW mid north coast, when he vanished without a trace on September 12.

He had been wearing his favourite red and blue Spider-Man costume.

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Donohoe helped with the SES search for William but was arrested four days later and charged with the unrelated sexual assault of two cognitively impaired young men between the late 2000s and 2014, news.com.au reports.

He was convicted of five charges, being three of aggravated sexual assault and two of sexual assault — take advantage of impairment.

Donohoe was jailed for five-and-a-half years with a non-parole period of three years.

He appeared today at the NSW Coroner's Court in Lidcombe at the inquest into William's suspected disappearance and death.

"I'd just like to point out that I have a cognitive impairment so could you take it very slow," Donohoe told counsel assisting the coroner, Gerard Craddock SC.

Deputy state coroner Harriet Grahame said: "If you have any difficulty understanding something, you speak directly to me."

The balding man was wearing a light pink short-sleeved shirt, black tie, grey pants and a dark belt.

He told Mr Craddock he remembered heading to Benaroon Drive — the street where William was last seen — to help with the search in the late afternoon of September 12, 2014.

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"I've been bashed in jail and everything so my memory is not 100 per cent," Donohoe said.

He said he was briefed in the car on the way to the suburban street but couldn't remember a second briefing at about 4pm upon arrival with his search group, called Taree 56.

"The place was like a football match, the amount of people that were there," Donohoe said.

He said they "went down to the river" to search for the boy and he finished his shift after midnight.

"I had to go to work the next day … and I was exhausted," he said.

Donohoe participated in an electronically recorded interview at Wagga Wagga police station at 1.32pm on November 13, 2018 with officers including Detective Senior Sergeant Mark Dukes.

Vision of the interview was played to the inquest today.

In the video, Donohoe refused to answer when asked to state his name and date of birth as the interview commenced.

He was also accompanied by a disability advocate in the room.

Detective Dukes said: "I'm going to ask you some questions about the disappearance and suspected murder of William Tyrrell on the 12th day of September, 2014."

Donohoe remained silent.

The disability advocate asked to interject, stating: "The solicitor advised that this recording would just be to ask if he consented to this recording".

The detective said he appreciated that, and offered a further explanation to Donohoe.

"The purpose of this interview, Mr Donohoe, you've been instructed, you've been given legal advice not to say anything, so we're going to record that however there are a number of allegations," he said.

Ms Grahame excused Donohoe after the interview was played on Friday.

Earlier this week, the inquest heard evidence from Donohoe's former boss, Sharon Starr.

Ms Starr, who ran the Woolworths petrol station at Lakewood, described his demeanour as "creepy".

She also said teenage schoolgirls from the nearby bus stop wouldn't go into the petrol station ship because they found him too "creepy".

"It was embarrassing," she said.

Donohoe slept in his white van parked at the local swimming pool or Kendall showgrounds at the time, Ms Starr said.

His van was searched by police in 2018 in a shed on the Donohoe family's property. The inquest continues.