The case of missing boy William Tyrrell will be handed to the NSW coroner with an inquest proposed for next year to “further the investigation” into his disappearance.

On the fourth anniversary of William’s disappearance, NSW Police announced that investigators have been speaking with Deputy NSW Coroner Harriet Grahame ahead of the proposed inquest.

In a statement, NSW Police said investigators in the case “would like to acknowledge the continued strength and courage of William Tyrrell’s families today”.

“Over the past year, investigators have continued to explore lines of inquiry in an effort to find out what happened to William, including a large-scale forensic search,” it said.

The deputy coroner has requested a brief of evidence, the statement said, which would be provided by the end of the year.

The inquest will be “an opportunity to test information and evidence gathered by Strike Force Rosann and further the investigation”.

“This is another step in ensuring answers are provided to William’s loved ones,” the statement said.

The then-three-year-old William was playing in his grandmother’s yard at Kendall on the NSW mid north coast when he vanished on September 12, 2014. He was three.

A large scale search of bushland near his grandmother’s home was wrapped up in July by a team of specialist officers led by the homicide squad.

Police at the time said while the search had not located William or evidence of him being in the search areas, Strike Force Rosann detectives gathered information relevant to the investigation.

Police earlier said they were convinced someone in the tiny NSW mid-north coast town knew more about William’s disappearance than they were letting on.

They also said their focus group of potential suspects had narrowed to just a handful – although they were tight-lipped about specific numbers and identities.

Detective Chief Inspector Gary Jubelin called on anyone who had seen suspicious activity in the area to come forward.

-with AAP