SALT LAKE CITY — Jurors have found a Ferron man guilty of killing his mother and brother, but called one of the deaths aggravated murder and the other manslaughter.

Seth Gordon Peterson, 26, was accused of shooting and killing his mother, Susan Peterson, 45, and his brother, James Peterson, 23, on Nov. 2, 2016, in a field near a farmhouse outside Hiawatha, Carbon County.

Peterson's attorneys, Rudy Bautista and Stephen Howard, told jurors during the trial that Peterson was responsible for shooting his mother and brother, but was experiencing "meth psychosis" and believed he was facing two "demons."

"We presented all the evidence that he was impaired and in a meth psychosis and had no consciousness that they were really his mother and brother," Bautista said. "It's not illegal to kill demons, and that's what he thought he was doing. Clearly, he was wrong."

But rather than murder, Bautista argued his client was guilty of manslaughter.

Prosecutors maintained at trial that despite the drugs, Peterson knew what he was doing and had knowingly killed his mother and brother.

After four days of trial and three hours of jury deliberations in Price, jurors found Peterson had committed manslaughter when he shot and killed his mother, but when he killed his brother 30 to 60 seconds later, it was aggravated murder.

Bautista said he is baffled by the split verdict and believes the same standard should apply to both killings. The defense team is now looking into whether the judge could amend the verdict and sentence his client instead on two counts of manslaughter, Bautista said. Otherwise, they will appeal the verdict.

A search warrant unsealed on Dec. 16 revealed Seth Peterson was paranoid in the days leading up to the killings, believing police were following him and his phone was bugged.

Susan Peterson — a mother of 15 children ages 28 to 3 at the time of her death — and her son, James Peterson, had gone to the farmhouse to pick up Seth Peterson on the day of their deaths.

Susan Peterson was shot and killed when she approached Seth Peterson, according to prosecutors. When James Peterson got out of his truck to check on his mother, he, too, was shot.

According to charging documents, other members of the Peterson family were nearby or present during the shootings and heard Seth Peterson say, "I just shot my mom in the (expletive) face," according to charging documents.

After the shootings, Seth Peterson took his brother's truck and drove off, approaching another man and insisting, "You have to help me hide two bodies," while pushing a rifle into the man's chest, the charges state.

Related:

Mother of 15 and son killed in Carbon County; 2nd son arrested

A mother of 15 and her adult son were shot and killed by another son of the woman near a ranch in a remote area of Carbon County Wednesday, according to sheriff's investigators.

That man, Peterson's uncle, said on the witness stand that Peterson told him he had killed demons, and those were the bodies he needed to bury, according to Bautista.

When the man pushed the gun away and tried to detain Peterson, Peterson grabbed a crowbar and hit him several times, "narrowly missing his head and significantly injuring his left arm," charges state.

Seth Peterson was arrested following a car and foot chase. The sheriff said several high-powered rifles were recovered from the scene.

Peterson was charged in 7th District Court with two counts of aggravated murder, a first-degree felony and capital offense, though prosecutors in January opted not to pursue the death penalty if Peterson was convicted. The charge still carries a potential prison sentence of life in prison without the possibility of parole.

Jurors also found Seth Peterson guilty Thursday of attempted aggravated murder and aggravated robbery, both first-degree felonies, and failure to stop at the command of police, a third-degree felony.

Sentencing is scheduled for Feb. 7.

Bautista said many members of Peterson's mostly tight-knit family, including his father, were present throughout the trial and agreed that the killings were manslaughter, not murder.

Following James Peterson's death, a family member posted a message on the man's Facebook page as if it were from James, blaming drugs for the shootings.

"I know it was the drugs, not you. Mom forgives you. She knows it was the drugs, not you. Make the world happier for me, now that I have passed," the family member wrote.

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