The Law Council of Australia warned NSW ICAC is prone to "show trial" hearings in public, under the leadership of Gladys Berejilklian's now-partner.
The former NSW Premier stepped down last month, the same day the NSW Independent Commission Against Corruption confirmed it was investigating her conduct. Public hearings will begin on October 18.
In a 2019 submission over the federal government's plan for a national corruption watchdog, the LCA called for investigative hearings to be held in private. It warned public hearings, inevitably causing a media firestorm, did not afford subjects the normal presumption of innocence during "what is going to be an investigation only".
Arthur Moses SC was LCA president at the time, before going on to represent Ms Berejiklian at a 2020 ICAC hearing into her disgraced ex-boyfriend Daryl Maguire. The pair have been in a relationship since early this year.
"It has been a valid criticism that public hearings conducted by state anti-corruption bodies such as ICAC in NSW can take on the flavour of a 'show trial'," the submission read.
"[They can] attract an undue amount of media attention in a forum where the concerned person has limited means of defending themselves against prejudicial material."
Ms Berejiklian maintained a "close personal relationship" with Mr Maguire, even after he resigned from NSW parliament over a corruption scandal. Phone calls between the pair were played during the public hearing into his conduct.
ICAC said it only holds public hearings, or discloses ongoing investigations, when it served the public interest. The Chief Commissioner and at least one other Commissioner were required to sign-off on a public hearing.
But the LCA called for Commonwealth findings to be made public only if the commission decided conduct could be criminally prosecuted.
It pointed to Queensland's watchdog, where only crime investigation hearings could be made public, as its preferred model. Even then, a public hearing could not be unfair to the subject, and would need to make the investigation more effective.
Then-attorney-general Christian Porter last year unveiled the government's proposal for a federal corruption commission, which would exempt public servants and politicians from being grilled in public.
The Coalition has flatly-rejected calls to adopt a NSW model for federal parliament.
But speaking to Channel 10 this week, shadow attorney-general Mark Dreyfus lashed the proposal as "more of a lapdog than a watchdog".