Fresh details about the execution of Antoun emerged on Monday with the arrest of gangland kingpin Farhad Qaumi, who police allege was behind an unprecedented spate of murders, shootings and extortions last year when the Brothers 4 Life gang descended into internal warfare.

Qaumi, who was appointed "general" of Brothers 4 Life last year by founder and supermax inmate Bassam Hamzy, and his younger brother Mumtaz Qaumi, 29, allegedly ordered low-ranking member Navid Khalili to shoot Antoun on December 16, last year.

It's believed the alleged shooting was related to sour construction industry deals and Brothers 4 Life were contracted to carry out the hit.

Mumtaz informed Khalili that he had taken a $200,000 contract to kill Antoun, court documents obtained by Fairfax Media reveal.

During a series of secret meetings around Sydney, Farhad Qaumi allegedly gave Khalili a silver revolver, Antoun's Strathfield address and instructions to kill him that night.

Antoun was shot five times on the doorstep of his Strathfield home in front of his six-year-old twin daughters. His partner, Teagan, yelled out at her husband not to open the door just as the bullets rang out, court documents state.

Antoun's friend and business partner, notorious construction industry figure George Alex, attended Burwood Local Court on Monday to see the Qaumi brothers face murder charges.

Mr Alex, who is preparing to give evidence to the royal commission into trade union corruption regarding kickbacks to corrupt union officials, said he was there to support his close friend. 

Antoun was part of a business venture with Mr Alex, providing scaffolding and labour hire for projects including the Barangaroo development.

Gang members have told police that Farhad Qaumi was a fiery, unpredictable gang leader who would have members "savagely beaten" if they didn't obey his directions, court documents state.

Qaumi had an unlikely right-hand woman, Amanda Crowe, 32, from Dulwich Hill, who was also charged on Monday with the murder of Mahmoud Hamzy in Revesby Heights on October 29 last year.

Qaumi, leader of the gang's Blacktown chapter, was desperate to kill Mohammed Hamzy, leader of the Bankstown chapter, because he had been told by Ms Crowe that Hamzy was planning to kill him first, court documents state.

The chapters had turned on each other late last year because Farhad was attempting to exert stronger influence over the entire gang, police allege.

Conflicts over drug deals, territory and extortion descended into dozens of shootings, knee-cappings and two murders.

When Mohammed Hamzy was overheard by Qaumi during a phone call referring to his Afghan-dominated Blacktown chapter as "Afghan dogs", the internal rumblings exploded, court documents state.

It is alleged Ms Crowe told the gang members the best time to carry out the hit on Hamzy and drove three men to and from the Revesby Heights crime scene.

The hooded men snuck up to the garage on Bardo Circuit and opened fire on a group of men. Mohammed escaped through a side door and survived but his cousin, Mahmoud, was killed.

Farhad was charged on Monday with conspiring to murder Mohammed Hamzy, murdering Mahmoud Hamzy and soliciting his younger brother, Jamil, 22, to do the shooting.

Zemarai Khatiz, lawyer for Ms Crowe and Qaumi, said outside court that the prosecution case was "weak" and based on evidence from one former gang member who has since rolled over to become a police witness.

"The [witness] has given a statement to the police nearly a year after the alleged offence. There are serious reliability and credibility issues," Mr Khatiz said.

Qaumi is already in custody on almost 50 charges including firearms offences and murder attempts. Ms Crowe is facing separate charges of ordering shootings on three other Bankstown chapter members on behalf of Qaumi.

Farhad, Mumtaz and Jamil Qaumi and Ms Crowe were all refused bail in Burwood Local Court on Monday.