Ex-cop loses bid to toss drug-dealer murder conviction

Evidence that crooked cop Roger Rogerson allegedly admitted planning other murders was correctly excluded from a joint trial over the slaying of drug dealer Jamie Gao, the High Court has found.

Rogerson and Glen Patrick McNamara were both sentenced to life imprisonment in 2016 for the murder in May 2014, when Mr Gao was lured into a darkened storage shed in Sydney's south and shot dead.

They also were jailed for stealing 2.78kg of methamphetamine with a street value of up to $19 million from the 20-year-old student.

Both failed to overturn their convictions and sentences in the NSW Court of Criminal Appeal with Rogerson, one of the Australia most notorious crooked cops, also losing a bid to appeal to the High Court.

On Wednesday, a panel of five High Court judges unanimously dismissed McNamara's challenge to his conviction.

He claimed that evidence of two conversations he had with Rogerson showed he feared for his life and acted under duress, and was not part of a joint criminal enterprise to enact the murder.

"The exclusion of the evidence left McNamara forensically disadvantaged and the tribunal of fact dispossessed of evidence consistent with innocence," his lawyers said in submissions to the High Court.

"The exclusion of this evidence precipitated a manifestly unfair trial."

In dismissing McNamara's appeal, the High Court found portions of these conversations were correctly excluded from the jury as they were deemed prejudicial to Rogerson.

Roger Rogerson being escorted to a prison van
Roger Rogerson is claimed to have admitted killing or conspiring to kill six other people.

"(There) are strong reasons of principle and policy to support a judicial discretion to exclude evidence of an accused where its probative value is outweighed by its prejudicial effect on another co-accused," the judges wrote.

There was no unfettered "right" for a co-accused to adduce all evidence relevant to their defence, they found.

In one alleged conversation from February 2014 about a potential book about Rogerson's life, he is claimed to have admitted killing or conspiring to kill six other people.

In a second conversation in May 2014, just after Mr Gao was shot in the storage shed, Rogerson allegedly threatened McNamara.

"Get up and f***ing help me you weak c*** or I'll leave you on the floor lying next to him," McNamara claims Rogerson said.

"He pulled the f***ing knife first, get up and help me or you'll be as dead as him."