In an extraordinary opening address to the murder trial for McNamara and Rogerson in the NSW Supreme Court on Tuesday, Mr McNamara's barrister, Charles Waterstreet also told the jury that his client had nothing to do with Mr Gao's drug dealing.

Instead, he said, McNamara had become involved with the 20-year-old because he was writing a book about Asian triads called The Ice Age about Asian triads selling the methamphetamine drug known as ice.

"Glen McNamara says that he's not guilty," Mr Waterstreet said as his client and Mr Rogerson sat in the dock.

"He says that he saw Roger Rogerson pull out the gun that he had a discussion with Mr Gao about the drugs and that Mr Rogerson shot Mr Gao in cold blood."

"Glen McNamara says that he knows nothing about having any gun in the shed or when he came into the shed. He had no idea he would pull a gun on Mr Gao. The was at all times, from beginning to end, the property of Mr Rogerson."

Mr Waterstreet - a Fairfax Media columnist - went on to say that, after killing Mr Gao, Mr Rogerson pointed the gun at his client and "threatened to kill him and his family".

"Mr McNamara has two daughters and Mr Rogerson knew that. Mr Rogerson threatened to kill Mr McNamara and threatened to kill his daughters if Mr McNamara did not comply."

He said that Mr McNamara was in fear that Mr Rogerson would carry out his threat and that his actions from that point were conducted under "duress".

These actions, according to the Crown case, involved dragging Mr Gao's body out of the storage shed and into a station wagon, and then taking him out in a boat and dumping the body off Cronulla the next day.

In response to the Crown's claim that Mr McNamara had met with Mr Gao on a number of occasions before the murder, Mr Waterstreet claimed that his client was researching a book about Asian triads.

He alleged that Mr Gao had been a member of the Sydney-based Asian triad Sing Wah prior to his death, and that Mr McNamara was writing a book about the role of the triads in importing and selling the drug ice.

"Mr Gao was a valuable source for Mr McNamara as a writer and he kept notes of all his meetings with Mr Gao," Mr Waterstreet said.

"The activity of Mr McNamara is one of innocence and one of duress. And one wonders - what do you do?"

Mr McNamara and Mr Rogerson are accused of murdering Mr Gao on May 22 last year in a south-west Sydney storage shed.

The trial continues.