Australian taxpayers are providing Transfield Services with $1.2 billion over 20 months to operate the detention facilities on Nauru and Manus Island.

It’s a huge cost to the public purse, requiring maximum accountability and transparency.

Earlier this year there was a damning report from the Moss inquiry about what had been happening on Nauru. So you’d have thought that when Transfield executives appeared before a Senate committee this week they’d have been well briefed to provide detailed answers to questions.

Instead their performance was woefully inadequate. Even the most basic questions had to be put on notice.

With allegations of rape, sexual harassment, bartering for sexual favours and women afraid to go to the toilet, the gender break down of staff was an obvious question they’d be asked. It was not one, however, that the executives could answer.

Nor could they throw light on how often the power failed. “I would take that on notice because it has changed over time,” said Derek Osborn, executive general manager of Transfield’s logistics and facilities management.

Pressed by Labor’s Kim Carr for at least a general indication, Osborn said it failed from “time to time” but couldn’t be more specific. Kate Munnings, chief executive operations of Transfield Services, broke in to explain that Osborn had a lot on his plate – he oversaw “a large business”.

Osborn couldn’t say whether he first heard of allegations of sexual exploitation before or after the Moss review. That had to go on notice too.

And it was not possible to get specifics on the day about the number of complaints about accommodation, facilities and staff.

The impression given was that either the Transfield executives had come extraordinarily ill-prepared or that they wanted to put as much as possible off to written replies.

Mullings said more than once that they had appeared on “short notice”. That hardly washes. Transfield knew after the Moss report and the March establishment of the Senate inquiry into the Nauru centre that it would be called. Surely a very detailed brief would have (or should have) been prepared and kept up to date. Transfield’s May 1 submission to the inquiry said it would welcome the opportunity to have its personnel attend the inquiry.

Executives of Wilson Security, which is contracted by Transfield to provide security services, also appeared at this week’s hearing and, while taking some questions on notice, had a good deal more information at their fingertips.

Answers eventually come through the questions-on-notice route, but there’s not the chance for immediate probing, as happens when they are given on the spot. However Transfield is going to be recalled.

After the hearing (which also took evidence from Save the Children) Immigration Minister Peter Dutton complained that Labor and the Greens had “combined to ensure only one point of view was presented”, accusing them of delaying proceedings so that there wasn’t time for the Immigration Department to appear.

“The department’s evidence would clearly be an inconvenient truth for this Labor-Greens witchhunt,” he said. (The department will get to be heard, in detail, later in the inquiry, as will whistle blowers.)

Dutton’s claim about “only one point of view” seemed to rest on some odd logic. You’d think that the department and the firm it contracts, Transfield, would have a broadly similar point of view.

The minister went on to say the department would co-operate fully with the committee but added that “this stunt should be seen for what it is - nothing more than a waste of time and taxpayers money”.

Dutton was absolutely ‘on message’. The government’s policy is to keep the public in the dark, as much as possible, about what happens at Nauru and Manus.

Allegations forced it belatedly to have the Moss inquiry, and it undertook to implement its recommendations. Mostly, however, it just wants to plug any possible sources of independent information and, where it can, to demonise those who try to probe, most notably the Greens.

Dutton, a former policeman, says he has “zero tolerance for any form of criminal activity” and all allegations of serious assault, including sexual assault, reported to the department are referred to the authorities for investigation. This declaration of the minister’s “zero tolerance” should be seen as nothing more than a statement of the obvious – it would be news if his position were anything else.

The Moss report found many asylum seekers apprehensive about their safety, and noted under-reporting (for various reasons) of sexual and other assaults – although it also said that when formal complaints had been made contract service providers had for the most part acted appropriately in dealing with them. It found both reported and unreported allegations of sexual and other physical assault on minors.

Moss found no substantiation for allegations that Save the Children staff ordered out of Nauru by the Immigration department had been fomenting trouble.

One difficulty in how the situation on Nauru tracks post Moss is that the government’s secrecy means there is relatively little media reporting on what’s happening. The picture must be filled in patchily, relying on leaks.

Given both the problems and the information void, there should be an independent ombudsman (who’d have to be appointed by the federal government), based on Nauru, who monitored both complaints and conditions, and reported regularly to federal Parliament. But don’t hold your breath for that.

Listen to the latest Politics with Michelle Grattan podcast, with guest, Nick Xenophon, here or on iTunes.