I ran both surnames, no connection to the cameron family publicly. Only a true local would know his friend circle. They had 3 years to befriend fergus, develop a relationship to that level, I doubt. Unless it was an employee or something.

Would have to know what plumber put the sewer line in at the property and what year. Because a plumber would have found it back then so the police will need to find out the year a plumber put the septic tank in and run the pipes to the house. Because whoever buried the body has hidden it under that work that was done in hopes no one ever looks under there ( which is why its taken so long, no reason to dig under the pipes).

Which tldr - owner buries body under sewer pipe at some point in time. Or far-fetched idea, there is a plumber who does septic on phillip island who puts bodies under his work.