Three Arrested, Including 17-Year-Old Girl, in Triple Homicide of California Parents and Friend

Three people, including a 17-year-old girl, were taken into custody Sunday in the triple homicide of a couple and their friend at a house in Fullerton, California, PEOPLE confirms.

The killings triggered a missing persons search for the 17-year-old daughter of one of the murder victims. Police would not disclose whether the 17-year-old in custody was the same person as the couple's daughter.

"It was a traumatic scene for our officers to walk into," Fullerton Police Department Sgt. Jon Radus tells PEOPLE. "It is our hope these arrests will bring some comfort to the community and bring some peace to the families that were affected by this absolutely unthinkable crime."

Josh Acosta, 21, and Frank Felix, 25, and the 17-year-old girl were taken into custody Sunday morning on suspicion of killing Jennifer Goodwill Yost, 39, her 34-year-old husband Christopher Yost and the couple's friend, Arthur William Boucher, 28. Charges are expected to be filed Tuesday, Radus says.

Of the couple's 17-year-old daughter, Radus says, "I can't comment on whether or not [the person in custody] was her but I can tell you that our focus is really on the two children that were in the residence," says Radus.

Radus says investigators "are looking at what the connection may or not be between the 17-year-old juvenile as well as the adults in connection with the house," he says. "We do not believe this was a random act of violence. We believe that the individuals who committed this crime specifically sought out this residence and the people inside."

There were no signs of a break-in, he says.

Police received a call around 8:20 a.m. on Saturday from the couple's six-year-old girl reporting that her parents had "died." When police responded to the 400 block of South Gilbert Street, they found all three bodies in different rooms with "significant trauma," says Radus.

Radus says the time of the killing is still under investigation.

Inside the home, police also discovered the couple's two daughters, six and nine. "It was a grisly crime scene and just to imagine two children to have to wake up expecting to see mom or dad and start their Saturday morning like most kids do to see what they saw would be difficult for anyone in law enforcement let alone two children," Radus says.

The two children are now with family members, he says.

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Shortly after the bodies were discovered, detectives learned that Katlynn was missing from the family home.

"Our investigators were unable to locate her throughout the day, through various investigative means as well as trying to reach her on the phone," says Radus. "After exhausting all of our possible leads on her we asked for the public's help in locating her about 8:30 p.m. Saturday."

On Sunday morning at 8:45 a.m. Felix was picked up in Sun Valley, a suburb of Los Angeles County. Acosta was taken into custody in Fort Irwin, California.

Radus says Katlynn was found unharmed in Los Angeles County on Sunday morning but wouldn't say if the teen was found with Felix.

'One of the Most Devastating Cases'

Neighbors described Christopher Yost as a loving father who enjoyed playing outside with his young daughter's, according to the Orange County Register.

On her website, Jennifer Yost described herself as a "very outspoken person."

"I am very proud of what I believe in and speak freely about my beliefs," she wrote.

At a candlelight vigil on Sunday night, Boucher’s uncle, Salvador Mineo, described his nephew as a "good kid" who worked at Mountain High and Taco Bell.

"Just the wrong place, the wrong place," he told the Register about Boucher.

"We do know he stayed at the residence from time to time and he was well known to all of the family members," says Radus. "Certainly wrong place and wrong time, that is for sure."

Boucher's mother, Kimberly Gracier, told the Register Jennifer Yost was having issues with her daughter over the teen's desire to have a relationship with an older man.

"It just seemed there was always something going on with the teenager," she said, according to the Register.

"I have been in law enforcement for 15 years and it is one of the most devastating cases I have been a part of," says Radus.