WASHINGTON — Sex, money and "power" led an Idaho man to murder his first wife and two of his second wife's children in a "doomsday plot", prosecutors have alleged.

Chad Daybell is accused of killing ex-wife Tammy Daybell, as well as Joshua "JJ" Vallow, 7, and Tylee Ryan, 16.

The children's mother, Lori Vallow Daybell, was sentenced to life in prison for their murders last year.

Daybell, 55, faces the death penalty if convicted. He has pleaded not guilty.

At the start of Daybell's trial on Wednesday, prosecutors said that he and Ms Vallow believed her children were "dark spirits" and "zombies" and murdered them in 2019, approximately a year after the pair met at a religious event.

Prosecutors claimed the two were having an affair together and came to view Mrs Daybell as a potential obstacle.

"When he had a chance at what he considered his rightful destiny, he made sure that no person, no law would stand in his way," prosecutor Rob Wood said.

"His desire for sex, money and power led him to pursue those ambitions and this pursuit led to the deaths of his wife and Lori's two innocent children."

After a long search, the remains of the children were found buried on Daybell's property in June 2020.

One of the children had been dismembered and burned, while the other was bound.

Mrs Daybell died of asphyxiation in October 2019, 17 days before Daybell married Ms Vallow at a ceremony in Hawaii.

Wood said that jurors will be shown "extended text messages to reveal his mindset and his motivations".

The attorney defending Daybell, John Prior, said expert witnesses would testify that his client's DNA was never found on the children's remains.

Instead, he sought to shift blame to Ms Vallow's brother, Alex Cox, who died in 2019. At the time of his death, police were investigating an incident in which Cox shot dead his sister's fourth husband, Charles Vallow.

"Whenever there was a problem or threat, you will hear testimony that Alex Cox came to the rescue," Prior said, adding that Cox's DNA was found on a piece of plastic alongside one of the children's remains.

Additionally, Prior claimed there was no evidence to suggest that Mrs Daybell's death was the result of foul play.

Daybell has also been charged with conspiracy to commit murder and faces insurance fraud charges stemming from life insurance policies he had taken out.

The judge in the case, Steve Boyce, sentenced Ms Vallow to three consecutive life terms without the possibility of parole in July 2023.

The trial is expected to last approximately nine weeks. — BBC