A team of five Australian Federal Police officers has been assembled to investigate rape allegations raised by Brittany Higgins.
But deputy commissioner Neil Gaughan will not say whether the alleged perpetrator has been interviewed.
"Natural justice has to be held here in relation to this particular issue," he told ABC radio on Wednesday.
"Of course, this person that has allegedly undertaken any crime is not obliged to be actually subjected to an interview, they have the right to remain silent.
"It's up to them, it's a matter for them, that's the way our democracy is and the way our laws have been crafted."
Ms Higgins alleges she was raped by a male colleague inside a ministerial office in Parliament House after a night out in 2019.
The former Liberal staffer initially decided not to pursue a police complaint, fearing her job could be affected.
But Ms Higgins re-engaged with the AFP about the alleged rape in February.
Four investigators assigned to her case are being overseen by an AFP detective-inspector.
"We will follow the evidence to where it takes us," Mr Gaughan said.
"We've got to get this right, clearly, and we will be methodical.
"We will work through the evidence, we will work with the DPP and when we are ready and when they are ready, we will make some further public announcements about it."
Mr Gaughan would not say how long the investigation might take.
"How long is a piece of string," he said.
"I don't want to put a timeline on it - I think that's really dangerous - I don't want to put pressure on investigators.
"My job is to provide them with time and space to do their job and that is my intention."
Mr Gaughan said he would not provide "blow-by-blow" details on progress of the case but any major milestones would be accompanied by public media releases.
"We'll just have to see where that takes us in the coming weeks."
Australian Associated Press