The NSW Supreme Court trial of Brothers For Life leader Farhad Qaumi​ and his brother Mumtaz Qaumi​, who are accused of ordering the murder of Mr Antoun, heard the victim had a drug debt to crime figure Pasquale Barbaro​.

​Barbaro was shot dead in Earlwood, in Sydney's south, on Monday night.

"Did [a witness] tell police that on one occasion Pasquale Barbaro told [the witness] he and his brother ... went to Mr Antoun's to kill him, but when they knocked on the door, his wife answered so they didn't go through with it?" Farhad Qaumi's barrister John Stratton, SC, asked officer-in-charge Detective Sergeant Peter Smith.

"Yes," Detective Sergeant Smith said.

The debt to Barbaro and his associates related to millions of ecstasy pills, the court heard.

Barbaro was shot dead as he left the house of construction industry figure George Alex in Larkhall Avenue at 9.45pm.

Justice Peter Hamill, who is hearing the Qaumi trial without a jury, remarked that the allegations about the earlier attempt to kill Mr Antoun could not be put to Barbaro.

Under cross-examination, Detective Sergeant Smith said there was no other evidence about the earlier attempt to kill Mr Antoun.

Barbaro's death came a day before he featured heavily in the Qaumi trial.

His voice was heard on intercepted phone calls with Farhad Qaumi, and photographs of the men sitting in The Star casino were tendered as evidence.

The court was told police approached Barbaro to make a statement about the Antoun case, but he refused.

The Qaumi brothers have pleaded not guilty to the murder of Mr Antoun, who was shot four times when he went to the front door of his Strathfield home on that evening in December 2013.

The gunman and the getaway driver, neither of whom can be identified, have pleaded guilty to their roles in the shooting.

The trial continues.