Shot in the leg, Sydney bodybuilder Hedi Ayoub sought shelter behind a tree in a south-western Sydney park. But there was no escape.

Omar Rajab, now 24, pursued a wounded Mr Ayoub before he fired a fatal shot into the victim's neck.

In the NSW Supreme Court on Friday, Rajab was jailed for at least 15 years and six months for murdering Mr Ayoub at Salmon Reserve in Punchbowl in June 2015.

In delivering her sentence, Justice Elizabeth Fullerton described the killing of Mr Ayoub, 22, who was shot four times, as "callous in the extreme".

Rajab pleaded guilty to the murder earlier this year.

Mohammed El Chami, 26, and brothers Ebrahim Allouche, 30, and Bilal Allouche, 24, pleaded guilty to lesser charges related to the killing.

According to an agreed statement of facts, Ebrahim drove Mr Ayoub to the park where they met Bilal and El Chami.

Moments later, Rajab arrived in another car. He extended a gun through the passenger side window and shot Mr Ayoub in the leg before continuing to fire shots as he pursued him through the park.

A witness reported hearing a male voice yelling: "You're a kelb, you're a kelb." "Kelb" is the Lebanese word for "dog".

"Omar, Omar, don't do it!" a witness also reported hearing.

In evidence, Rajab claimed Mr Ayoub was a standover man who had threatened to hurt him and his family after he had intervened in a drug debt dispute.

Rajab said his friends had arranged a meeting with Mr Ayoub to smooth over tensions between the pair. But when Rajab arrived, he said, Mr Ayoub was acting aggressively. Rajab said he fired a warning shot in Mr Ayoub's direction and unintentionally struck him in the leg.

"I understand this was the wrong thing to do but I was in a bad way mentally," Rajab said.

"The situation was taking over my life, plus I felt uncomfortable about bringing my friends into it. I was concerned for their safety considering Mr Ayoub's prior violent behaviour."

Rajab said he continued to fire warning shots at Mr Ayoub. When he saw Mr Ayoub reach for his bumbag as he sat under a tree, Rajab said he panicked and shot him again.

"I still can't believe I shot him. I wish I could have my time all over again," Rajab said.

"The whole incident was surreal."

In her sentence, Justice Fullerton was highly critical of the Crown's failure to challenge any of Rajab's evidence.

"The Crown's attitude generally to the sentence proceedings of all four offenders has been of little assistance," she said.

 The Allouche brothers and El Chami were charged with murder, but the charges were replaced with far less serious ones earlier this year.

The brothers pleaded guilty to being accessories after the fact to murder for disposing of Mr Ayoub's mobile phone.

Bilal was jailed for six months and Ebrahim for four months.

El Chami was jailed for three months for withholding information about the murder from police.

As the three have already served time in custody, they walked free after the sentence was delivered.

Rajab will be eligible for parole in 2031.