Trial begins for suspect in 2016 Fullerton triple-homicide, a case that has links to 'furry' community

Oct. 30--Trial began Monday for a 23-year-old Army mechanic who, prosecutors say, fatally shot a Fullerton couple and their friend as they slept because he believed the couple had been abusing their daughter. The defendant's attorney told jurors the man was autistic and had been "duped" into committing the 2016 slayings.

According to prosecutors, Joshua Acosta was stationed at Fort Irwin when, he told police, he decided on his own to kill Christopher Yost, 34, and his wife, Jennifer Yost, 39, to "free" his friend, the couple's then-17-year-old daughter, Katlynn Goodwill Yost.

Deputy District Attorney Troy Pino told jurors that Acosta said the third victim, Arthur "Billy" Boucher, 28, was "collateral damage" because he was not expected to have been there at the time.

Chris Yost, with his wife Jennifer.<br />(Courtesy of GoFundMe page)

In the early hours of Sept. 24, 2016 Acosta, then 21, allegedly entered the Fullerton home on South Gilbert Street and shot Boucher as he slept on the couch in the living room then proceeded to shoot Jennifer Yost in her bed and Christopher Yost as he tried to run out a door into the backyard, according to prosecutors.

Officers were alerted to the killings by one of the couple's young daughters, ages 6 and 9. Prosecutors played the 911 call the 6-year-old made after discovering her parents' bodies.

"Where's your mom or dad?" a dispatcher asked the girl.

"My dad is outside in the backyard dead and my mom is in the bed dead," the girl replied.

Family members of the victims in the courtroom cried as they heard the recording while Acosta sat mostly expressionless in a white and blue striped button-down shirt.

Arthur WilliamBoucher, 28, was killed at his friend's Fullerton home. Christopher and Jennifer Yost, who lived there, also were killed. (Photo Courtesy of Salvador Mineo)

When officers arrived, they found the bodies. The 17-year-old was missing.

"They don't know if Katlynn is kidnapped, is dead or part of this," Pino said.

After a day of searching, the girl was found and arrested along with Acosta and his friend, co-defendant Frank Felix, 27, of Sun Valley. Felix is set to be in court on Nov. 9 for his alleged role in the crime. Acosta was found with three bullet casings on him. The teenage girl was never charged.

Attorneys said there was tension between the parents and teenage girl because she was underage and wanted to date Felix.

The girl claimed that Yost, her stepfather, had molested her and her mother had physically abused her.

In a recording of his confession, Acosta told police: "That family is a twisted, wretched cesspool and it's a festering wound. I cauterized that festering wound."

The three became friends through the so-called furry and brony communities. "Furries" like to dress up as animals and take on personas while "bronies" are men who have an affinity for the children's cartoon show "My Little Pony." The victims also were involved in the furry community.

Pino said the teenage girl has been granted "use immunity," which means her testimony cannot be used against her. Prosecutors said she claimed she didn't know that her parents were going to be killed.

"There was a plan to emancipate her from her family because she was unhappy with her parents," Pino said. Acosta told police in an interview that it was his idea alone to murder the parents.

As for the abuse: "Is it true, is she lying? We may never know," Pino said.

Acosta's attorney, Adam Vining, said his client was involved with the brony community and often carried a pony character with him when he went out to do his Army combat exercises.

Vining spoke generally about autism, saying "Autistic people tend to be naive, emotionally immature."

Though he did not elaborate, Vining said of Acosta: "He was duped."

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