Police believe Farhad Qaumi, 34, had also been trying to find out the addresses of three other detectives, who worked on the investigation that brought down his violent street gang.

Qaumi is currently on trial in the NSW Supreme Court for the murder of construction industry figure and standover man Joe Antoun in Strathfield in December 2013.

Qaumi, the former Blacktown chapter leader, was recently convicted of a string of violent offences - including manslaughter and conspire to murder - following a mammoth criminal trial.

It is understood police learnt during that trial of a supposed plan to target four detectives, including from the Middle Eastern Organised Crime Squad. It played out in the NSW Supreme Court for six months and ended in November.

Fairfax Media has been told Qaumi managed to get the home address of one detective and was offering a contract around criminal circles to have the officer killed. However, Qaumi struggled to find anyone reckless enough to agree to carry out the plan.

Even among Sydney's hardened criminals, murdering a police officer has generally been a no-go zone. An informant learnt of the plan and made police aware of the danger posed to the officer's life.

Officers went on to fortify their homes, boosting security measures, as a result.

The Robbery and Serious Crime Squad is investigating the plan and how one of Sydney's most notorious gang figures allegedly managed to find out where the detective lived.

If the allegations are proven, it will be a chilling example of the reach some of these criminals have, despite being locked up in the state's highest security prisons.

Qaumi, nicknamed "The Afghan", was appointed as the BFL's "general" in 2012 by gang figurehead and Supermax inmate Bassam Hamzy.

Violent infighting erupted within the gang in 2013, with a string of tit-for-tat shootings between the Bankstown and Blacktown chapters.

Farhad along with brothers Mumtaz, 31, and Jamil Qaumi, 24, were found guilty of conspiring to murder Bankstown chapter leader Mohammed Hamzy in October 2013.

While Hamzy - known as "LC" or "little crazy" - was the intended target, it was his cousin Mahmoud Hamzy who was fatally shot when gunmen opened fire at his Revesby Heights garage.

The three Qaumi brothers were also found guilty of manslaughter.

There were also convictions for other non-fatal shootings.

Asked about the allegation he was hatching a plan to kill police officers, Qaumi, via his lawyer, told News Corp: "I've never tried to kill a police officer. That has never crossed my mind."