Joshua Acosta admitted to using a shotgun to kill Christopher and Jennifer Yost, and their friend, Arthur Boucher. But Acosta's lawyer claims the couple's stepdaughter, Katlynn Goodwill, is the real villain.

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An Army mechanic who confessed to killing a "furry" couple and their friend in Southern California, allegedly to protect the couple's teen daughter from sexual abuse, has been convicted of murder.

Joshua Acosta, 23, now faces life in prison without the chance of parole for the 2016 shooting deaths of 34-year-old Christopher Yost, his wife, 39-year-old Jennifer Yost, and their friend, 28-year-old Arthur Boucher in Fullerton.

Acosta met the Yosts, along with Jennifer Yost's 17-year-old daughter Katlynn Goodwill, in the “furry” community - people who like to dress up as and act like animals, according to the Orange County Register.

Acosta told investigators he was trying to protect Goodwill, who testified at his trial that Christopher Yost, her stepfather, had molested her on a weekly basis for eight years. Goodwill said she was going to tell her mother about the abuse on the night of the murders and had enlisted the help of Acosta and Frank Felix, another friend, to help her run away, but didn't know Acosta was going to kill anyone.

Defense attorney Adam Vining disputed the teen's claims and argued she manipulated Acosta, who he says is autistic, into killing her mother and stepfather simply because she wanted them gone.

“I know she is not on trial, but she is the villain,” Vining said of the Goodwill, who testified under immunity.

joshua acosta

Goodwill admitted to previously lying to authorities about who allegedly abused her and who she told about it, according to the Orange County Register. Even with the uncertainty surrounding the abuse allegations, prosecutors argued that Acosta was still resposnsible for the killings.

During an interview with police, a recording to which was played at trial, Acosta called the Yost family a “twisted, wretched cesspool” and a “festering wound.” He described using a shotgun to shoot Boucher, who he referred to as "collateral damage," in the head as he lay sleeping on the couch. He told cops he then shot Jennifer Yost between the eyes in her bedroom before gunning down Christopher Yost as he ran away.

Felix is being tried separately for his alleged role in the triple homicide.

The Associated Press contributed to this report.

[Photo: Fullerton Police Department]