On a crisp Saturday morning two years ago, Scott Parkin stepped from a café in the inner-Melbourne suburb of Brunswick to find himself surrounded by six burly, casually-dressed men. Identifying themselves as federal police and immigration officials, they told the shocked US citizen that he was being taken into "questioning detention".

Parkin was taken to a high-security prison facility and placed in solitary confinement, where he remained for five days. At no stage was he charged with a crime, nor was he given any explanation for his detention, beyond the information that a "competent authority" considered his presence in Australia to be a "direct or indirect" risk to national security.

Until then, Parkin's Australian sojourn had shared much in common with the itineraries of the thousands of backpackers who swarm to Australia's east coast every year. He took surfing lessons, toured a crocodile farm, spent time volunteering on an organic farm and made new friends in Brisbane, Sydney and Melbourne.

As a committed peace activist and proud Texan, Parkin was also devoted to spreading the word about his Houston-based group's campaign to expose military contractor Halliburton and its subsidiary KBR as key "pillars of support" for the invasion and continuing occupation of Iraq. He found a willing audience for his views at anti-war meetings, on community radio and at the Brisbane and Sydney Social Forums.

Unbeknownst to Parkin, something he had said or done during his travels had sparked a flurry of official activity apparently aimed at making sure his first visit to Australia would also be his last. Precisely which actions or what utterances led to Parkin's removal from Australia remains a secret of such great consequence that the Coalition government waged a Federal Court battle in defence of this secrecy for close to two years.

Two days prior to Parkin's detention, the Australian Security and Intelligence Organisation (ASIO) had advised the Minister for Immigration that his presence constituted a "direct or indirect risk" to Australian national security. This triggered the cancellation of his tourist visa, automatically rendering him an "unlawful non-citizen" under the Commonwealth Immigration Act and compelling his immediate detention pending deportation.

After five days in immigration detention, Parkin was escorted to Melbourne Airport and marched onto a plane bound for Los Angeles. Upon arrival, his Australian escorts presented him with a bill for $AU11,700 – the total cost of his incarceration and removal, including flights and accommodation for his security escorts – courtesy of the Australian government.

Storm of Protest

Parkin's treatment sparked a storm of protest across Australia. Within hours of his detention, activists, civil liberties groups and non-government organisations sprang to his defence.

The public outrage at Parkin's detention could not have come at a worse time for Attorney-General Phillip Ruddock, the Minister responsible for ASIO's actions. Just a few days before Parkin was detained, Prime Minister John Howard had announced the introduction of a sweeping package of counter-terrorism laws, which entailed a significant broadening of ASIO's powers.

But in a display of national security "me too-ism" that foreshadowed the federal Opposition's acquiescence on the startling case of Dr Mohamed Haneef, then Opposition leader Kim Beazley declared his support for the cancellation of Parkin's visa.

With the Opposition's support declared, the Attorney-General remained tight-lipped about exactly what Parkin was alleged to have said or done to receive one of the handful of adverse security assessments resulting from the many tens of thousands of security checks conducted by ASIO each year. Mr Ruddock would say only that the assessment was related to ASIO's responsibility to protect Australia from "politically motivated violence, including violent protest".

In late 2005, lawyers acting for Parkin began Federal Court proceedings to have the adverse security assessment quashed. As a first step, they sought a discovery order to determine precisely what Parkin is alleged to have said or done to warrant the adverse assessment. (Parkin's lawyers are also acting for Mohammad Faisal and Mohammed Sagar, Iraqi refugees who faced indefinite detention on Nauru after receiving similar adverse assessments. Faisel and Sagar have since been released).

Concealed and Protected

Over the past two years, ASIO has gone to extraordinary lengths to keep the reasons for Parkin, Sagar and Faisal's adverse security assessments secret, even to the extent of appealing a routine order to confer with Parkin's lawyers on the grounds that simply providing a list of documents relating to the case would irreparably damage national security.

While the initial public outrage has been long since been quelled by the glacial pace of the court proceedings, the puzzling case of Scott Parkin demonstrates how supposed mechanisms of accountability are serving to conceal and protect ASIO from scrutiny at a time when the domestic spy agency has more power and greater resources than ever before.

These mechanisms of accountability include ASIO's reporting relationship with the Attorney-General, the right of the Opposition leader to be briefed on national security matters, the oversight of the Inspector General of Intelligence and Security (IGIS) of the scrutiny of Senate Committees, including the Parliamentary Joint Committee on Intelligence and Security.

In December 2005, the unclassified version of a report by the current IGIS, Ian Carnell, dismissed claims published in The Australian newspaper that Parkin had planned to teach "tactics of violence", including throwing marbles under the hooves of police horses. The front page article, which appeared days after Parkin was removed from Australia, was "not a reliable guide to the assessment", Carnell said.

But, while acknowledging that "the precepts of natural justice would point to providing Mr Parkin with the details of the security assessment and allowing him to respond and suggest ways in which the evidence and considerations might be tested", Carnell refused to provide even the broadest outline of the reasons for ASIO's actions. When weighed by Carnell against considerations of national security, these fundamental precepts – which include the right of the accused to know what is alleged against him or her – simply gave way.

In October 2005, ASIO's Director General of Security Paul O'Sullivan gave evidence before a Senate Estimates hearing that Parkin had not been involved in violent or dangerous protest in Australia. But the adverse security assessment, O'Sullivan said, was related to Parkin's "behaviour subsequent to his arrival in Australia", and not to his activities in the United States. O'Sullivan continued, "I can be quite clear in saying that there was no consideration of any particular matter coming from abroad in [Parkin's] case".

In May 2007, this story appeared to change when counsel for O'Sullivan told the Federal Court that ASIO did not rely solely on information related to Parkin's activities in Australia.

In a Senate Estimates hearing two days later, when Greens Senator Kerry Nettle asked O'Sullivan whether he stood by his previous evidence before Estimates, O'Sullivan refused to respond on the grounds that the matter was before the court. The Committee Chair then ordered Senator Nettle to discontinue her line of questioning.

But thanks to legislation passed by the Howard government – the National Security Information (Criminal and Civil Proceedings) Act 2004 – the Attorney-General has the power to intervene in cases like Parkin's to prevent particular evidence from being heard in an open court. He can do this simply by conclusively certifying that the appearance of certain witnesses or evidence would prejudice Australia's national security.

With a change in government, the Parkin case could be a critical test not only of the courts' ability to hold ASIO accountable for its actions, but of a new Attorney-General's willingness to inconvenience Australia's ever-expanding domestic security apparatus by upholding the fundamental precepts of natural justice which underpin our legal system.

Iain Murray is the author of "Where the Bloody Hell Are You? A report on the Australian Government's detention and forced removal of US citizen Scott Parkin", available at <www.scottparkin.org>.