A criminal profiler helping in the year-long search for missing boy William Tyrrell has revealed details of his suspected kidnapper and what she says was likely an opportunistic crime.
Dr Sarah Yule says her investigations suggest possible explanations for the then three-year-old's disappearance from the front yard of his grandmother's Kendall home on the NSW mid-north coast are limited.
"I've assisted with a lot of missing persons cases but this case presents several significant, unique challenges," Dr Yule said in comments released by police.
"There really is a limited number of possibilities that can account for William's disappearance."
The NSW police force's senior forensic psychologist said there was "only a narrow window of opportunity" to take the little boy.
"The area where William vanished is on the edge of the township near a dead-end street," Dr Yule said.
"So if no one but William's parents and grandmother knew in advance of his visit to Kendall, then you would have to have some other reason to be there and take that opportunity; either visiting, residing or working in the vicinity."
Detective Inspector Gary Jubelin, who's heading the investigation, said the inclusion of a behavioural specialist on the strike force had been invaluable.
"In cases like these we need to get into the headspace of the person who took William, why they did it, what makes them tick," he said.
"The kidnapping occurred on a Friday around 10.30am. It was broad daylight and whoever abducted him risked being seen from the balcony of William's grandmother's home as well as neighbouring properties."
Police are appealing for new information on the case, a day after more than 2000 people marched through Kendall to raise awareness of William's disappearance.
