The New South Wales State Coroner has granted public prosecutors the right to keep five documents relating to the bail of Lindt Cafe gunman Man Haron Monis secret from the inquest into the Sydney siege.

Counsel for the families of siege victims Katrina Dawson and Tori Johnson have argued for the documents, detailing communications between a senior homicide detective and a solicitor working in the Office of the Director of Public Prosecutions, to be tendered in the inquest.

It is understood those communications detail concerns homicide investigator Detective Senior Constable Melanie Staples had regarding Monis's release on bail in December 2013 on a charge of being an accessory to the murder of his ex-wife.

Counsel for the Johnson family, Gabrielle Bashir, argued that it was unfair to withhold such critical information.

"This represents a very unfair position," she told the inquest.

"These documents, in our submission, should be released ... so this witness can have a fair and appropriate testing of her evidence without hands being ties behind our backs."

Counsel assisting the inquest, Jeremy Gormly, agreed with Ms Bashir's submission and argued that it was in the public interest to release the documents to the inquest.

"There is a real public benefit in all of these documents being released," he told the inquest.

"It is [within the power] of the DPP to waive privilege over these documents for the public interest."

Counsel for the DPP, David Buchanan, argued against releasing the documents, maintaining its position that they were confidential because they were subject to legal professional privilege.

State Coroner Michael Barnes accepted that argument on all but one of the documents, and said he had no right to over-rule the DPP's privilege.

"I recognise this may cause difficulty for the inquest and the parties in ascertaining why the bail application was dealt with as it was," he said in his judgement.

"It is simply the effect of the law relating to legal professional privilege.

"There's nothing I can do about that."

Monis was on bail for a string of sexual assaults and being an accessory to murder when he took staff and customers hostage at the Lindt Cafe in December last year.

At a preliminary hearing last week, the DPP successfully applied to have dozens of documents and communications between police and its solicitors withheld from the scope of the inquest.

The DPP solicitors who handled Monis's bail applications are expected to give evidence at the inquest this afternoon.