Hannah Quinn was heard to say "what the f*** have you done?" after Blake Davis brought the weapon down on Jett McKee's skull as he was on his hands and knees, prosecutor Chris Taylor said on Monday.

"The deceased was covered in his own blood and brain matter witnesses may tell you," he said.

He was giving the crown opening address at the NSW Supreme Court trial of Quinn, 26, and Blake, 31, who have pleaded not guilty to murdering the 30-year-old in August 10, 2018 at Forest Lodge.

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

Mr Taylor said Mr McKee had a gambling addiction, poker machines in particular, and had been using the drug ice.

He and a Mr O'Connor needed money and wanted to rob a drug dealer.

Mr O'Connor knew Quinn and Davis to be drug dealers and they became the target, the prosecutor said.

Mr O'Connor drove to their address before Mr McKee got out with a balaclava, knuckledusters, and a "blank-firing" pistol.

Mr Taylor outlined evidence expected to be given by witnesses including a neighbour who looked down from a fourth floor residence after hearing an argument.

She allegedly saw a person being shown out of the door before he fell backwards and then ran away followed by a female and a man who had what looked like a lamp pole.

"The female accused caught up with that man, and you'll hear evidence that she pulled him to the ground," Mr Taylor said.

The male accused followed shortly after, before raising above his head with both hands a samurai sword, while "the man was on his hands and knees", so the Crown alleges.

Another neighbour would testify that Davis was wearing only his boxer shorts and had a samurai sword he recognised as having been displayed in the couple's home.

A building worker was expected to say he saw the man who was being chased hunched over the middle of the road trying to stand up before the female tried to fling him away and the other man brought the sword down on top of his head.

A question for the jury would be whether Mr McKee had anything in his hand at the time he was struck with the sword, Mr Taylor said.

Numerous witnesses told police they didn't see him with anything in his hands at that time, he said.

"That may tell you they did not see at any point any gun or pistol in the possession of anybody including the deceased."

The couple allegedly ran home and hid the sword before leaving with more than $21,000 cash, two mobiles phones, six nunchucks and a gold imitation gun.

Police found the "stashed" items nearby in a narrow alley in an Uber Eats bag.

The couple went "on the run" for some days, staying at hotels, before a solicitor arranged for them to go to a police station.

Davis allegedly told a friend that someone had come into his house and tried to rob him.

"They had a gun and hit me in the face with brass knuckledusters, it hurt," he allegedly said.

The friend said Davis had about five samurai swords, which were displayed on a stand, since he was about 13 and had been into martial arts since he was 14.

Mr Taylor will continue his address on Tuesday.

Australian Associated Press