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

Susan Peterson, 45, and James Peterson, 23, were killed by Seth Gordon Peterson, 25, just before 6 p.m. in a field near a farmhouse outside of Hiawatha, Carbon County Sheriff Jeff Wood announced Thursday. All three are from Ferron, Emery County.

Seth Peterson was arrested following a short car and foot chase and was booked into the Carbon County Jail for investigation of two counts of aggravated murder, attempted murder, theft of a vehicle and failure to stop at the command of law enforcers.

As of Thursday afternoon, the sheriff said investigators did not have a motive for the killings.

"We know that the mom had gone out there to pick up her son (Seth)," Wood said. "I'm not really sure why they were out there at this time. There are a couple of different theories."

Wood said several high-powered rifles were recovered from the scene.

The Petersons' LDS bishop released a statement Thursday on behalf of the family.

"Susan was a loving mother of 15 children, ages 28 to 3. She was very active in the community and in her church. Susan was very service oriented and was always taking care of other people. She was a very intelligent person, always thirsting for knowledge in bettering herself and her family. Her family was her whole life and she supported them in all they did.

"Susan always thought of others before herself. Her husband states that she would often go without new clothing and other necessities in order to make sure her children had what they needed. She never wanted for herself.

"James was kind-hearted and would give you the shirt off his back. He was very personable, kind, respectful and thoughtful of others," the bishop wrote.

After the shootings, investigators say Seth Peterson drove away in a vehicle. Deputies responding to 911 calls of someone being shot spotted the car leaving the ranch area and a chase ensued for about 5 miles. At the end of the car chase, Peterson got out and ran but was quickly tracked down and "peacefully captured," Wood said.

Deputies had responded to another call of a "suspicious incident" at the ranch about three hours before the shootings, but the sheriff said there was no threat at that time.

Investigators were walking through the area again Thursday with eyewitnesses to get a better idea of what happened. Wood said there were at least three areas where deputies were focusing their investigation: the area where the chase ended, a field a few hundred yards away from the farmhouse, and around a ditch.

According to a GoFundMe page set up by family members, as well as social media posts by many relatives and friends, Susan Peterson was a mother of 15 children. Nine of those children still live at home.

"She is an inspiration to all who know her and have been touched by her light and love," one woman wrote on Facebook.

Peterson was involved with the mentoring group Limitless. Many of those who posted tributes and messages of condolence on social media knew her through that organization.

"I have been so deeply inspired by this woman. She was doing everything she could to be prepared to share her story on stage at our Limitless event in January," wrote one woman. "My heart is absolutely broken over the loss of this precious woman."

Although investigators have not released a motive for the killings, some who identified themselves as family members on social media noted that Peterson died while "trying to protect her children."

"She is a momma bear who lost her life protecting her children," wrote one man who identified himself as Peterson's cousin. "Susan is loved and will be missed."

Another person wrote: "Looks as though a son of hers was really hurting and struggling," making an apparent reference to Seth Peterson.

Susan Peterson's Facebook page states she graduated from high school in Emery County. One person remembered the family from when they lived in Parma, Idaho.

Hiawatha is an old mining town. Wood said the coal mine shut down in the early 1990s, but there are still residents who live in the town. The bodies were found several miles outside of town.

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