Of the many twists and turns in the Cleo Smith saga, a swift guilty plea by the man who abducted her is up there as one of the more surprising developments.

But one expert says the sheer weight of evidence against 36-year-old Terence Darrell Kelly meant there was only likely one outcome at Monday's court appearance in Carnarvon.

University of Newcastle criminologist Dr Xanthe Mallett says the strength of the case against Kelly meant a guilty plea was always likely, even with significant public interest in Cleo looming as a potentially distorting factor in proceedings.

"I wasn't surprised," Mallett told Sunrise on Tuesday.

"Even from what the public had been made aware of in terms of the evidence against him, it seemed that it was a very compelling case so I was expecting a guilty plea,"

Kelly's videolink admission from a Perth prison on Monday shocked onlookers, many of whom were expecting a lengthy, drawn-out legal process to follow accusations he took 4-year-old Cleo from a remote Western Australian campground in October and held her captive for 18 days.

Kelly had been arrested in Carnarvon in the early hours of November 3 — nearly three weeks after the young girl vanished from her family's tent at the remote Quobba Blowholes campsite.

The girl's disappearance made headlines around the world, with a special task force established and a $1m reward offered to help solve the case.

Cleo was ultimately found safe and alive nearly three weeks later in Kelly's locked house, after detectives forced their way in.

The Carnarvon man was charged with forcibly taking a child aged under 16 – which he has pleaded guilty to.

He is due to face the Western Australian District Court for a sentence mention on March 25.

Mallett said the guilty plea would "significantly reduce" the trauma on Cleo and her parents.

"They would have interviewed [Cleo] already, a child psychologist would have spoken to her," Mallett said.

"But this means they don't have to go to any more of that process and they can start to move on so I think for the family, this is a really significant change for them and hope to spot them peace.

"We need to put this to bed now. That little girl needs to move on and so does that family, so to leave them to deal with the trauma and hopefully they are receiving the assistance they need to do that."

- Alex Druce, news.com.au