Mr Collaery is accused of unlawfully sharing classified information about the 2004 bugging operation of negotiations to carve up lucrative oil and gas reserves in the Timor Sea.

Labor senator Kim Carr chastised the continued prosecution, asking how it could remain in the public interest after an ACT court found Mr Collaery was motivated by justice and Witness K received a three-month suspended sentence.

The DPP must be satisfied that any case it prosecutes is in the public interest.

Witness K's sentence and the case's impact on public confidence in the justice system are part of the prosecution's considerations about whether the case remains in the public interest.

Director Sarah McNaughton told Senate estimates on Tuesday the evidence she had seen and the seriousness of the alleged conduct warranted Mr Collaery's continued prosecution.

Attorney-General Michaelia Cash said the power she has to discontinue a prosecution is reserved for "unusual and exceptional circumstances" and it had never been used by any of her predecessors.

Senator Cash said any intervention by the attorney-general would constitute political intervention in an independent process.

Australian Associated Press