The probe into the leaking of confidential Foreign Affairs Ministry papers has been widened amid signs investigator Paula Rebstock has identified a "prime suspect" behind the leaks.
The Government was buffeted by a string of embarrassing leaks at the ministry earlier this year, as it worked on plans to cut jobs and entitlement.
The leaks, which included internal memos and details of staff pay, culminated in up to three Cabinet papers being handed to Labour foreign affairs spokesman Phil Goff.
They discussed restructuring plans, the future of the ministry's overseas posts, including in Europe, and its financial position. The Cabinet committee that was to discuss the papers had not met when Mr Goff revealed details in Parliament.
Prime Minister John Key indicated only about 20 people had access to the papers.
State Services Commissioner Iain Rennie said they were provided in confidence to senior officials at Mfat, the Department of the Prime Minister and Cabinet, the State Services Commission and Treasury.
He called in Rebstock to investigate the leaks and on May 4 set the terms of reference for the inquiry which covered the three papers, related documents and advice on how to improve the security of government information.
But in a previously undisclosed move, Rennie three weeks later amended his instructions to include "all the relevant background facts surrounding the development of the Mfat change programme".
That included "the environment within which Mfat was operating during this period" and "who may have been responsible for earlier unauthorised disclosures during the development of the Mfat change programme".
In his May 23 letter to Rebstock, released under the Official Information Act, Mr Rennie said he had always intended the inquiry to encompass a broad investigation, and he was making the change to avoid doubt.
It is understood the expanded brief has required many more interviews, delaying the final report.
But a departmental source said that should not be seen as a sign the inquiry would fail.
"There is a level of confidence in the Government that Rebstock is making progress and has identified one suspect - a key person," he said.
Can the ACT Party survive?Related story: ACT life support still on