Former detectives Roger Rogerson and Glen McNamara have been sentenced to life in prison for the murder of Jamie Gao.

Rogerson, 75, and McNamara, 57, were found guilty of murdering Mr Gao, 20, during a drug deal at a Padstow storage facility on May 20, 2014 and dumping his body in waters off Cronulla the next day.

In handing down the sentence, Supreme Court Justice Geoffrey Bellew said: "The joint criminal enterprise to which each offender was a party was extensive in its planning, brutal in its execution and callous in its aftermath."

"It is clear that the offenders acted with complete disregard for the life of another human being.

"The offending surrounding the deceased's murder was of an exceptionally high degree of seriousness."

Justice Bellew said just because Mr Gao was involved in the drug trade, he did not deserve to be shot and killed.

In sentencing submissions, New South Wales crown prosecutor Christopher Maxwell QC had called for life sentences, saying the men had killed for financial gain and it was no different to a contract killing.

The crown said the offence had been made even more serious because of their intention to "obtain and distribute a drug that is a scourge of our society".

That drug was methylamphetamine, known as "ice".

Lawyers for both Rogerson and McNamara have indicated the former detectives will appeal against their convictions and sentences for murder.

Jamie Gao's family pleased with sentence

In a statement, Mr Gao's family said the sentence was "the best outcome we, as Jamie's family, could have hoped for".

"To have these two men, who took Jamie from us, sentenced to essentially die in jail, is absolutely fitting," they said.

Mr Gao's family said Jamie was found guilty of criminal offences in the "court of public opinion". ( Supplied: Facebook )

"The courts can't lessen the term of Jamie's death or the impact that his death, the investigation and ensuing trial has had on our family.

"When it comes to losing a family member you love through murder, there is no real justice."

However, Mr Gao's family said it was disappointing there would be no chance for him to defend allegations of his involvement in criminal enterprise.

"There has been no opportunity to present evidence to clear Jamie's name of the alleged crimes he's been accused of committing as put forward at various junctures throughout the trial," they said.

"There was no burden of proof offered to him prior to finding him guilty in the court of public opinion."

But Mr Gao's family has still extended its thanks to authorities.

"We would however like to thank the police, the DPP and the courts for their efforts in putting Jamie's killers behind bars for what we hope is the rest of their lives."

Differing accounts of Gao's death heard during trial

During the trial, both men denied pulling the trigger and instead pointed the blame at each other.

McNamara's defence told the trial it was Rogerson who shot and killed Mr Gao before threatening McNamara and his family, forcing him to help dispose of the body.

Roger Rogerson (L) and Glen McNamara (R) murdered Jamie Gao in a secure shed. ( AAP )

Rogerson said Mr Gao was killed during a struggle with McNamara and the student was dead on the floor when he entered the shed.

Justice Bellew said he could not determine beyond reasonable doubt who shot Mr Gao, but that he was satisfied one of them had.

"The deceased was executed in cold blood, just as the offenders had planned," he said.

"Clearly, one of them shot the deceased."

The trial was told Mr Gao had a number of meetings with McNamara in the months before his death.

McNamara's claim that these meetings were for a book he was writing about Asian crime gangs was dismissed by prosecutors, who said McNamara and Rogerson were preparing for the killing.

Prosecutors told the court the crown did not have to prove which of the defendants killed Mr Gao, just that there was an agreement to kill or seriously injure the victim.

It took the jury just under a week to reach the verdicts.