"We're looking for anything that's foreign to the area, and anything that links to William's disappearance." 'High-risk' person of interest leads to change in search for William Tyrrell
This made me think of a plant taken into the area and settled over the grave as a sort of memorial marker as well as concealer.
A high risk POI maybe someone who is Subject of an order made under the high risk offenders act that NSW has. NSW Legislation
Tick, Tock...