Murdered Australian journalist Greg Shackleton (Images: AAP/MUP)

For decades, Australia's intelligence services have denied having any foreknowledge that the Balibo Five were at risk from Indonesian forces.

Intelligence services ostensibly only learnt shortly afterwards that the five -- journalists working in then-Portuguese Timor in October 1975, reporting on secret Indonesian military activity -- had been murdered by Indonesian special forces.

But Oil Under Troubled Water, a new book by Bernard Collaery, presents a strong case that Australian spies knew that Indonesia regarded the journalists as a "hurdle to be got over" before Indonesian military preparations could ramp up ahead of its December 1975 invasion, beginning a quarter-century occupation of the province.