By Julia Carlisle
SYDNEY, Sept 12 AAP - Senior NSW detectives have not given up on the investigation into the disappearance of Sydney boy William Tyrrell, as his family and foster family mark three years since he vanished.
The three-year-old was last seen playing in the garden of a home at Kendall, south of Port Macquarie, on September 12, 2014.
Detective Chief Inspector Gary Jubelin, who leads the homicide investigation, insisted on Tuesday the case was "very much ongoing".
"We will not give up on the investigation... (it is) currently very active," he told reporters in Sydney on Tuesday.
He said detectives believed William's disappearance had "human intervention", and reminded the public about the $1 million reward for information that leads to the recovery of the little boy.
"The information might be in the form of someone who has concerns about someone they know. Someone within their family. The way they react when his name is mentioned might cause suspicion. We are interested in speaking to those people. If we speak to those people, we can do it with the strictest of confidence."
Light has been shed on his short life in the past month, following a failed bid from the NSW Department of Family and Community Services to keep his in-care status private.
William's biological parents, Karlie Tyrrell and Brendan Collins, have also been named.
Det Insp Jubelin said William's foster-care situation has not impacted the investigation in any way.
"The foster care parents had custody of William at the time of his disappearance. They were bringing him up in a loving family and the situation between foster care and biological family played no part in his disappearance."
William's foster family took to Facebook on Monday to declare they'd never give up hope of finding him.
"William, we will never stop loving you," they said.
A renewed national campaign for information has also been launched this week in the hope someone will come forward with information for detectives.