The prosecuting solicitor who elected not to oppose bail for Lindt Cafe gunman Man Monis when he appeared in court on scores of serious sex charges two months before the siege had only been employed by the Director of Public Prosecutions for two months and had never dealt with a bail application in NSW, a court has heard.

A police officer from the NSW Sex Crimes Squad told the ongoing inquest into December 2014 siege that she had repeatedly urged the solicitor to apply for Monis' bail to be revoked when he appeared in court on 37 sex charges on October 10, 2014, but the solicitor decided not to do so.

These were the latest in a series of serious criminal charges including sending offensive letters to the families of dead Australian soldiers, accessory to murder and three other sex offences.

"He told me it would be futile," said Detective Senior Constable Denise Vavayis​, the officer in charge of investigating the sexual charges against Monis.

"I didn't agree, but I accepted his position as the solicitor with carriage of the matter," she said.

The inquest has heard that, in deciding not to apply for bail to be revoked, the solicitor, who cannot be named, had not realised that the accessory to murder offence and some of the sex offences had allegedly occurred while Monis was on bail.

Had the solicitor applied for bail to be revoked and made the magistrate aware of this fact, Monis may have been remanded in custody, in which case the siege would never have occurred.

A panel of experts who reviewed the actions of the DPP and police in relation to bail found that the solicitor should have done so given the apparent breaches of bail, the strength of the Crown case, and the number of charges Monis was facing.

Late on Monday it emerged that he had only been working for the DPP for two months and had never been involved in a bail application in NSW, though he had been involved in such proceedings in other states.

"Would it have made a difference [to how you dealt with the matter] if you had known that he had never been in a bail application in NSW before," counsel representing the family of siege victim Tori Johnson, Gabrielle Bashir, SC, asked Constable Vavayis.

​"He was the solicitor with carriage of the matter," the officer replied.

"But nonetheless you expected him to be experienced," Ms Bashir continued.

"It's not my job to make decisions for him, that's his domain," the officer said.

However, the inquest heard that Detective Vavayis and her police colleagues had also failed to realise that some of Monis's offences had occurred while he was on bail, and therefore had no communicated this fact to the solicitor.

The officer said that it was not "routine practice" for police investigating historical sex offences to check an accused person's bail history.

She also asserted that doing so was a "minute and exhaustive process" as information in the police database had to be cross referenced with that from the NSW court system.

"I didn't put two and two together," she said.

In his opening address, counsel assisting the inquest Jeremy Gormly said a breakdown of communication between the Commonwealth agency responsible for the offensive letters charges and the NSW Police may also have contributed to the oversite.

"It's hard not to note the consequences resulting from the lack of flow of information across jurisdictional boundaries," he said.

Mr Gormly also revealed that the shotgun used by  Monis was one of 250,000 guns that make up Australia's "grey" weapons market.

"The serial number indicates that the gun was of a kind manufactured oversees and frequently imported into America," Mr  Gormly said.

"But American authorities indicate that the gun was not imported into that country."

Mr Gormly said that after the gun was imported into Australia, it was probably sold by the Sydney gun wholesaler previously know as Fullers.

It was never registered, nor was it handed in during the compulsory gun buyback in 1996 that followed the Port Arthur massacre.

However, the inquest heard that despite it ultimately being used for criminal purposes it did not come from the black market which produces so many of the guns used by Sydney criminals.

Instead, Mr Gormly said, it became part of Australia's "grey market" – a collection of 250,000 fire arms that are generally used by sports shooters or farmers but have never been registered.

The inquest continues.