Her death would have brought “swift conclusion” to any financial entanglements, a prosecutor claimed.
Her death would have brought “swift conclusion” to any financial entanglements, a prosecutor claimed. Liam Kidston

Gas poison trial: He said ‘he would kill me and the children’

A HUSBAND is accused of an insidious and "elaborate" plot to kill his wife by manipulating the very air she breathed.

Robert Wayne Ridgeway pleaded not guilty on Tuesday to the attempted murder of Pepita Ridgeway and not guilty to an alternative charge of administering a noxious gas with intent.

Prosecutors accuse the American man of introducing nitrogen to a caravan at Doonan where his wife slept in July 2016.

Sunshine Coast woman Mrs Ridgeway was the first witness to give evidence at the Brisbane Supreme Court trial on Tuesday.

The couple were married for about 18 years and Mrs Ridgeway said the relationship was "up and down" and especially rocky from 2011.

She told jurors that in December that year, in Las Vegas, she complained when her husband went to get food at a hotel and returned to the room with nothing for her.

"And that enraged him. And he got very angry…it escalated to him yelling at us for twenty to forty minutes.

"During that time, he threatened that if I divorced him, he would kill me and the children."

She said the couple had three children together.

After living in the US, the couple moved to Doonan, where Mrs Ridgeway and her brothers owned a five-acre piece of land.

Mrs Ridgeway said her husband also owned a 185-acre property near Mackay.

She said the couple argued about money, a horse float, properties, and over the couple's 15 year-old daughter doing modelling.

She alleged Mr Ridgeway once grabbed her by the shoulder and pushed her up against a wall, his fist clenched.

Jurors saw an email prosecutors say Mrs Ridgeway sent to her husband on July 1, 2016.

"As you know, I have realized that we can no longer be together or live together," the email read.

Prosecutor David Finch said on July 4, Mrs Ridgeway went to see a lawyer about a separation or divorce.

And the same day, Mr Ridgeway bought a big cylinder of nitrogen gas in Maroochydore, Mr Finch said. And the next morning, Mrs Ridgeway allegedly woke up to the sound of hissing gas.

Mr Finch alleged Mr Ridgeway intended to deplete oxygen levels in the caravan to the point Mrs Ridgeway suffocated.

Mr Finch said any separation would have been difficult, considering the couple's intertwined lives and joint property interests.

"Pepita Ridegeway's death, her passing, would have brought a swift conclusion to all of that."

The trial continues.  -NewsRegional