A picture "more bristling with menace" can hardly be imagined for a young woman of 23, barrister Tom Hughes said in his opening address on behalf of Hannah Quinn on Tuesday.

The now 26-year-old and her boyfriend Blake Davis, 31, have pleaded not guilty in the NSW Supreme Court to murdering Jett McKee on August 10, 2018 in the middle of a street in Sydney's Forest Lodge.

Quinn also has denied a charge of being an accessory after the fact to murder.

The Crown has alleged the pair, said to have been drug dealers, chased the 30-year-old about 100 metres down the street before Quinn pulled him to the ground and Davis struck his head with the sword.

"The crown case, even assuming a home invasion and attempted robbery or actual robbery by the deceased in the present case, is the circumstances are the deceased was being chased away from the premises," Chris Taylor said.

Davis's barrister Margaret Cunneen SC said he was not guilty of murder or manslaughter, submitting he had been acting in defence of his girlfriend when he killed Mr McKee.

Davis had suffered multiple facial fractures after Mr McKee hit him while wearing knuckledusters after entering the home through an unlocked door and demanding valuables.

Mr Hughes said he himself was present when Quinn, who had just completed her certificate in early childhood education, took part in a six-hour police interview days after the killing.

This was "possibly one of the most harrowing and emotional accounts you will ever hear", he said.

Quinn was subject to the "most terrifying and completely traumatising" events at the hands of a man, who she had never met, in the sanctuary of her boyfriend's home.

Mr McKee was found to have a "toxic to lethal" amount of ice in his system, leading Mr Hughes to say he was "full as a goog" with the drug and also armed to the teeth with weapons.

Quinn told police a "really huge, scary guy" wearing a balaclava came in with a gun in his hand, saying he would shoot them, that he knew their relatives and wanted their stuff.

Quinn said she screamed before the man grabbed her handbag from her shoulder and ran out, with her following and grabbing it back when she caught up with him.

He tried to punch her, but missed, lost his balance and then was holding the gun up at her, she said.

"I was just frozen, that is when Blake ran up and he hit the guy," she said.

Mr Taylor has told the jury numerous witnesses told police they didn't see Mr McKee with anything in his hands at that time.

But Mr Hughes said the indications of malevolence - the gun, the balaclava and other items - were found near where he fell on the roadway.

Ms Cunneen said police found an amount of cannabis, and no ice, in the Forest Lodge home.

The issue of self-defence did not start on the street, but when Mr McKee entered the home, disguised and armed, when Davis was in bed wearing only his boxers.

After being punched and following them out on the street, he heard his girlfriend screaming and "did what he did in defence of Ms Quinn".

"Mr Davis's case was he was holding that gun."

The trial continues before Justice Natalie Adams.

Australian Associated Press