BOISE, Idaho (AP) — An Idaho jury has convicted Chad Daybell of murder in the deaths of his wife and his girlfriend’s two youngest children.

Thursday’s verdict marks the end of a years-long investigation that included bizarre claims of zombie children, apocalyptic prophesies and illicit affairs.

Now the jury will be tasked with deciding if Daybell should be sentenced to death for the crimes. The penalty phase of the trial was to begin later Thursday.

Prosecutors charged Daybell and his newest wife, Lori Vallow Daybell, with multiple counts of murder, conspiracy and grand theft in connection with the deaths of Vallow Daybell’s two youngest children, 7-year-old Joshua “JJ” Vallow and 16-year-old Tylee Ryan, in September 2019.

Prosecutors also charged the couple in connection with the October 2019 death of Chad Daybell’s wife, Tammy Daybell.

Prosecutors had said they would seek the death penalty if Daybell was convicted.

Daybell’s defense attorney argued there was not enough evidence to tie Daybell to the killings, and suggested Vallow Daybell’s older brother, Alex Cox, was the culprit.

Vallow Daybell was convicted last year and sentenced to life in prison without parole.

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The verdict, reached after six hours of jury deliberations, capped a complex trial that spanned nearly two months.

The nearly two-month trial now enters the penalty phase, with prosecutors attempting to show that the crimes merit a death sentence because they were especially depraved, heinous or cruel or that they meet one of the other “aggravating factors” detailed in state law. Daybell’s defense, meanwhile, will try to provide the jury with mitigating circumstances that could show the panel a lighter sentence is more appropriate.

The case began in September 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 Alex Cox in Arizona in July 2019; the brother told police it was in self-defense. He was not charged.

Vallow Daybell, her kids JJ and Tylee, and Cox subsequently moved to eastern Idaho to be closer to Daybell, a self-published writer of doomsday-focused fiction loosely based on Mormon teachings.

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 that she died of asphyxiation. Chad Daybell and Vallow Daybell married just two weeks after Tammy Daybell died, surprising family members.

Nearly a year after the children went missing, their remains were found buried on Chad Daybell’s property in eastern Idaho. Investigators later determined both children died in September 2019. Prosecutors say Cox conspired with Chad Daybell and Vallow Daybell in all three deaths, but Cox died of natural causes during the investigation and was never charged.

Prosecutors called dozens of witnesses to bolster their claims that Chad Daybell and Vallow Daybell conspired to kill the two children and Tammy Daybell because they wanted to get rid of any obstacles to their relationship and to obtain money from survivor benefits and life insurance. Prosecutors say the couple justified the killings by creating an apocalyptic belief system that people could be possessed by evil spirits and turned into “zombies,” and that the only way to save a possessed person’s soul was for the possessed body to die.

Fremont County prosecutor Lindsay Blake said Daybell, 55, styled himself a leader of what he called “The Church of the Firstborn” and told Vallow Daybell and others that he could determine if someone had become a “zombie.” Daybell also claimed to be able to determine how close a person was to death by reading what he called their “death percentage,” Blake said.

With these elements, Daybell followed a pattern for each of those who were killed, Blake said.

“They would be labeled as ‘dark’ by Chad Daybell. Their ‘death percentage’ would drop. Then they would have to die,” she said in her closing argument.

Blake also said Daybell manipulated Vallow Daybell and her brother, Cox, into helping with the plan, at times bestowing ‘spiritual blessings’ on Cox and warning Vallow Daybell that the angels were angry because she was at times ignoring him.

Daybell’s defense attorney, John Prior, rejected the prosecution’s descriptions of Daybell’s beliefs. He described Daybell as a traditional member of the Church of Jesus Christ of Latter-day Saints, a deeply religious man who talked about his spiritual beliefs every chance he could get.

Prior said police looked only for things they could use against Daybell rather than the actual facts of the case — and he claimed that the children’s late uncle, Cox, committed the crimes. He noted that Cox had previously killed JJ Vallow’s father in Arizona and that the two children were the only witnesses to that shooting. He also said Cox tried to frame Daybell by burying the slain children in Daybell’s yard in eastern Idaho.

Witnesses for both sides agreed that Chad Daybell and Vallow Daybell were having an affair that began well before Tammy Daybell died.

Defense witnesses included Dr. Kathy Raven, a forensic pathologist who reviewed reports from Tammy Daybell’s autopsy and said she believed the cause of death should have been classified as “undetermined.”

Chad Daybell’s son, Garth Daybell, told jurors he was home the night his mother died and that he heard no disturbance. He said he later felt like police officers and prosecutors were trying to pressure him to change his story, even threatening him with perjury charges at one point.