Three arrested, including a 17-year-old, in triple homicide in Fullerton

Fullerton police have arrested three people, including a 17-year-old female, in connection with a triple homicide at a residence from which a teenage girl was also reported missing and considered “at risk,” authorities said Sunday.

“The suspects and family are known to each other,” Sgt. Jon Radus told reporters at an afternoon news conference at the Fullerton police station. “This is not a random act of violence.”

Two suspects were identified as Josh Acosta, 21, of Fort Irwin, and Frank Felix, 25, of Sun Valley. The juvenile was not named because of the individual’s age.

All three suspects were in custody by 8:45 a.m. Sunday on suspicion of murder and conspiring to commit a crime, police said. No other details were disclosed about the investigation.

Radus would not say whether the juvenile was Katlynn Goodwill Yost, 17, whom police had identified earlier as the person who was missing from the house. But police did say that the teenager had been located and was unharmed.

The homicide victims were identified as Christopher Yost, 34; Jennifer Goodwill Yost, 39, who is the mother of Katlynn; and Arthur William Boucher, 28, a friend who occasionally stayed with the family.

Officers arrived at the house in the 400 block of South Gilbert Street on Saturday morning after receiving a phone call from another young girl who lives there, saying her parents were dead.

Police found the bodies of the victims, all of whom had suffered “significant trauma,” Radus said.

Police did not release any details about how the victims were killed, but said no weapons were recovered at the scene.

Two young girls were in the house and unhurt, according to authorities.

The girls, who are 6 and 9 years old, are safe and staying with relatives. It was the 6-year-old who called police early Saturday morning and told them her parents were dead, Radus said Sunday.

The girls are receiving counseling. “These children have been through an incredibly traumatic experience,” Radus said.

On Saturday, police described Katlynn, the 17-year-old, as “a missing/at-risk person.”

“We’re concerned about her welfare because she lives in a residence where three people were found deceased,” Radus said at the time.

Friends and neighbors at the scene Sunday morning said they had no idea who might have committed the killings or why.

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One neighbor said he heard a loud bang sometime after 11 p.m. Friday, but did not think much of it. A second neighbor said she was startled awake sometime before midnight by a single, loud noise, but went back to sleep.

Both neighbors asked that their names not be used.

Another woman in front of the house Sunday morning, who asked that she not be identified, described herself as a longtime friend of Jennifer Yost.

She said Yost was a stay-at-home mom, into crafts and cooking, who sewed some of her own clothes and occasionally made stuffed animals for the kids. The husband, Chris Yost, was a mechanic who worked on cars in the backyard, neighbors said.

Officers had been looking for Katlynn since 9 a.m. Saturday.

By Sunday morning, the crime scene tape had been removed, the TV trucks had left and the neighborhood appeared to be back to normal. Two candles stood on the front porch of the small house with an American flag and a Hawaiian lei hanging on the front door.

In the backyard, toys and a pair of pink child’s flip flops were abandoned on the ground. “I love you Mom,” was etched on the side of a cinderblock wall.

jack.dolan@latimes.com.

Twitter: @jackdolanLAT

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UPDATES:

Sept. 26, 11:08 a.m.: This article was updated with details on the suspects’ charges.

This article was originally published at 5:10 p.m. Sep. 25.