The grey Mazda was taken from a home at Gymea under a coronial order last Tuesday, police confirmed this morning.
It is undergoing forensic analysis, which is expected to take several weeks.
“This activity relates to inquiries and search operations currently being conducted in the Kendall area,” NSW Police said in a statement.
9News can confirm the seized car belonged to William’s now-deceased foster grandmother at the time of his disappearance.
It has since changed ownership.
Detectives are using a chemical that detects traces of blood and officers have also brought in a cadaver dog.
Hundreds of officers and dozens of Rural Fire Service volunteers are conducting a fresh search of the area surrounding the boy’s foster grandmother’s house in Kendall on the NSW Mid North Coast.
William disappeared from the home in 2014, when he was three-years-old.
Yesterday morning, NSW Police Commissioner Mick Fuller told 2GB: “I’m confident that the team who has the investigation at the moment can solve it.”
When asked whether detectives were focusing on anyone of interest, Mr Fuller added: “My understanding is, from the investigators, is that there is certainly one person in particular that we are looking closely at.”
Announcing the new operation on Monday, police confirmed they were looking for remains.
Aside from the house, police are also examining a bushland site about one kilometre away, clearing the scrub yesterday.
William, at the time aged three, disappeared from his foster grandmother’s property on Benaroon Drive in Kendall at about 10.30am on September 12, 2014.
Over the years, police have put pressure on several suspects who have since been ruled out.
