Serving police and intelligence officers should be granted legal immunity to step forward and give evidence to an independent judicial inquiry into the Martin Place siege, according to independent Senator Nick Xenophon.
Amid signs of growing momentum for a more extensive and arm's length inquiry into the circumstances surrounding Monday's deadly siege, the influential legislator has also praised Prime Minister Tony Abbott for his handling of the tragedy.
Senator Xenophon told Fairfax Media Mr Abbott's comments in the aftermath of the incident had provided comfort and reassurance to shocked Australians while also expressing the anger many people felt.
But he said the fact that several hostages were shot and two were killed demanded a more extensive inquiry than the six-week one already commissioned, which will be jointly led by the heads of the Prime Minister's and NSW Premier's departments.
There are also questions over ASIO's level of awareness and treatment of the gunman, Man Haron Monis.
"It beggars belief that this man was not on an active watch list," Senator Xenophon said.
Senator Xenophon said a judicial inquiry with the power to compel witnesses should be established but suggested such an inquiry could be initiated by the Parliament if not started by the government.
And he was no less conclusive about the appearance of shortcomings in ASIO's monitoring of Monis.
"Giving ASIO a bigger and bigger budget doesn't mean they doing a better job," he said, referring to the $630 million in extra funding allocated to the counter-terrorism fight this year.
"They're spending money on things like Witness 'K' in an East Timor commercial espionage case - where there was no suggestion of a national security threat or a risk to the safety of Australians - rather than on monitoring genuine threats to the community."
The extension of immunity would allow the inquiry to speak to analysts employed by ASIO to establish if there were concerns over the diversion of resources away from immediate national security threats, and if there had been resistance to dropping Monis off the watch list in 2009.
He said serving and former security officers should be free to come forward to an inquiry safe in the knowledge that they will not be putting their careers at risk, and that the judge would make sound decisions as to what information should be withheld from release in the interests of national security or the safety of ASIO and police personnel.
"They should be given complete immunity," Senator Xenophon said.
"The nation is still in collective shock, so it is reasonable that with so many unanswered questions, that people should want the most thorough process.
"There are so many armchair critics that I think it is proper that this be handed over to a proper judicial inquiry … questions need to be asked.
"If there's ever been an example of systemic failures in intelligence, this appears to be it."
The South Australian was supported in the call for immunity by University of New South Wales security academic Clinton Fernandes, who said coming forward without immunity would be "career suicide" for ASIO employees.
Dr Fernandes, a former Army intelligence officer, also said the terms of reference for the inquiry should be broad enough to consider whether the military action in Iraq had, in the opinion of ASIO analysts, altered the risk profile in Australia.
