Naman Shrestha
In 1984, when a high school student named Kirsten Costas was found murdered outside her family’s house, the entire community was shaken to its core. For several months, the police moved heaven and earth to get to the bottom of the case and find out the perpetrator behind the crime. A shocking confession cracked the case open and allowed the Costas family to get some closure. Investigation Discovery’s ‘Mean Girl Murders: Bad News Bobbies’ chronicles the decades-old murder case of Kirsten and the months-long investigation that ensued.
Bernadette Protti’s Jealousy Drove Her to Kill Kirsten Costas
Described as a polite teenager, Bernadette Protti was raised in a devout Christian household alongside her four siblings. As she attended Miramonte High School in Orinda, California, she made a name for herself. However, she was not as popular as one of her peers, Kirsten Marina Costas. Both of them were integral members of the swimming team and a prestigious volunteer group. Jealousy took over Bernadette when she failed to get selected for the cheerleading squad, but Kirsten made it to the squad. On June 23, 1984, Bernadette allegedly invited Kirsten to a dinner party, which turned out to be a tactic to lure her to meet with her. According to Bernadette, the latter got angry when she found out that there was no dinner.
As per Bernadette, Kirsten then went over to the nearby house of Alex and Mary Jane Arnold, telling them about what had happened. As per reports, when she failed to get in touch with her parents by telephone, Alex offered to drive her home. Soon after Kirsten got out of the car, she was ambushed by Bernadette, who attacked her with a large knife and stabbed her multiple times before fleeing the scene. She eventually succumbed to her injuries at a local hospital. During the initial phases of the investigation, Bernadette gave an unverified alibi but passed a polygraph test. Due to a lack of evidence against her, the case remained unsolved for six months until she surrendered herself to the police in December 1984.
The killer teenager made a detailed confession to the detectives, saying, “I thought that she was going to tell everybody at school that I was really weird. I can’t explain it. I don’t understand it. It was, like, if I had been thinking straight, it would never have happened. . . . Afterwards, I was just so horrified and sick.” She told them how Kirsten used to hurt her by allegedly throwing mean comments at her. “She had never liked me, but I thought she was OK. The thing that got me mad was it hurt and I couldn’t change…Like, looks or money or popularity or things,” she added. She also revealed that after the murder, she washed off the large knife with which she stabbed her classmate to death. After the confession, Bernadette Protti was charged with Kirsten’s murder and ordered to remain in custody.
Bernadette Protti Moved Out of State After Her Release From Prison
Since she was just 15 years old at the time of the murder, Bernadette Protti was tried as a juvenile. During her trial in March 1985, she did not claim innocence but asserted that it was a second-degree murder. The defendant said that she had not planned the murder and found the large kitchen knife by chance, as it was in her car to cut vegetables. The family of Kirsten Costas did not believe that someone would keep such a long knife just to slice vegetables. In the end, Bernadette was convicted of second-degree murder after rejecting the prosecution’s arguments for first-degree murder.
She was sentenced to the maximum term of nine years in the custody of the California Youth Authority, much to the disappointment of the Costas family. Kirsten’s mother, Berit, stated, “My heart is empty. I ache. I’m half a person. She probably will be given her freedom in a few years. I ask the people of California, is this justice?” After serving less than eight years of her sentence, Bernadette Protti was released from prison on parole on June 10, 1992. A couple of years later, she was released from supervision, after which she reportedly changed her name and moved out of California with her family. Ever since then, she has stayed away from the limelight, leading a private life.
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