Accused murderer admits account 'unusual'

A man accused of raping and murdering a 66-year-old Sydney woman when he was a teenager admits his account of the sexual assault is "most unusual".

The man, known as BL, has pleaded not guilty to the murder and sex assault of Doris Fenbow who was discovered lying face down amid billowing smoke in her Sydney apartment on September 3, 1988.

BL, who was just shy of his 18th birthday when Ms Fenbow died, says he was forced to sexually assault her and had nothing to do with her killing.

"It is without a doubt an extraordinary account of sexual intercourse," defence barrister Bill Neild told the NSW Supreme Court on Wednesday.

"My client does not say anything other than it's most unusual."

Ms Fenbow's feet and legs were charred, she was naked from the waist down and she had bruising to her eyes.

The trial has heard that a profile of DNA taken from Ms Fenbow and compared with a swab given by the now 45-year-old BL in 2014, occurs once in every 100 billion people in a theoretical population.

On the evening of September 2, Mr Neild said BL had gone out to get cigarettes when he was punched by the now dead Kevin Hayward and dragged into a darkened unit.

Once there he says he was sexually assaulted by Mr Hayward and forced on top of Ms Fenbow's body.

Giving his closing address, Mr Neild conceded it was an unusual story but said "that is not the test".

"It falls to the crown to prove it couldn't reasonably happen that way."

He told the jury that Hayward had been sexually abusing his client since he was 12.

As a consequence, Mr Neild said his client felt like the older man had a hold over him.

"It seemed like he had a power over me," BL has said of Hayward.

Neild told the jury: "be very careful - from the comfort of this courtroom in 2015 - of being critical of a 17-year-old boy who has been abused throughout the bulk of his childhood, about what he did or did not do back then".

The trial continues.