Adopted son helped murder parents

A man has told a jury how his adoptive father yelled "you bastards" and "put up a decent struggle" as he and his friend allegedly killed him.

David Weightman and Terry Mark Donai have been accused of murdering Bill Weightman, 51, and Pamela Weightman, 50, at their Glen Alpine home in January 2000.

Weightman was giving evidence today at the NSW Supreme Court trial of Donai, who has denied his involvement in the murder.

Prosecutor Margaret Cunneen SC alleged the couple were drugged and suffocated by their adopted son and Donai, before their deaths were made to look like a car accident.

The jury has been told that Weightman, who was 21 at the time, has admitted murdering his parents for his inheritance.

He told the jury he became friends with Donai, who was 10 years older than him, about three to four months before his parents were killed.

Weightman said he would joke with his parents how he would inherit their home and valuable pre-school business and they would tell him not to look at it like that.

"It was very light ... nothing sinister about it," he testified.

Weightman said he had told Donai: "If they are gone. I get everything".

During one conversation, Donai told him he (Donai) would kill them and Weightman could get him a particular motorbike.

"I said I didn't want them to feel any pain and I don't want to be involved, because I didn't want to have nightmares or be haunted by it," Weightman said.