BOISE, Idaho (AP) — Opening statements are expected Wednesday in the trial of an Idaho man charged with killing his wife and his then-girlfriend’s two youngest children in an unusual case rooted in extremist religious beliefs.

Chad Daybell, 55, is facing charges of first degree murder, insurance fraud, and conspiracy to commit murder and grand theft in connection with the deaths of Tammy Daybell, 7-year-old Joshua “JJ” Vallow and 16-year-old Tylee Ryan. Last year, their mother, Lori Vallow Daybell, received a life sentence without parole for the killings.

Prosecutors say the couple justified the three killings with doomsday beliefs, part of an elaborate scheme to eliminate any obstacles to their relationship and to obtain money from survivor benefits and life insurance. Vallow Daybell referred to her two youngest kids as zombies, one friend testified during her trial.

Chad Daybell was a member of the Church of Jesus Christ of Latter-day Saints and self-published fiction loosely based on its teachings.

In fall 2019, he tried to fraudulently collect on his late wife’s life insurance policy, and Vallow Daybell continued to collect both children’s social security benefits after they died.

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Chad Daybell has pleaded not guilty to the charges, and the trial is expected to take more than two months. Prosecutors said they will seek the death penalty if Daybell is convicted.

The grim story began in the fall of 2019, when extended family members reported the two children missing and law enforcement officials launched a search that spanned several states. The subsequent investigation took several unexpected turns.

Vallow Daybell and Chad Daybell were having an affair when both of their spouses died unexpectedly, investigators said. Vallow Daybell’s husband was shot to death by her brother in Arizona in July 2019; the brother told police it was in self-defense.

Several months later, in October 2019, Tammy Daybell died. Chad Daybell initially told police she was battling an illness and died in her sleep, but an autopsy later determined she died of asphyxiation. Vallow Daybell and Chad Daybell married just two weeks after Tammy Daybell died, surprising family members and drawing suspicion from authorities.

Friends later told detectives that Vallow Daybell and Chad Daybell believed they had been reincarnated and were tasked with gathering people before a biblical apocalypse.