The 80s: The Deadliest Decade S01 E03 (Kirsten Costas)

Backstory Kirsten was the daughter of rich parents Arthur and Berit Costas. Costas attended Miramonte High School and was a member of the school’s varsity swim team and the cheerleading squad. Events On June 23, 1984, Costas was lured with a phony invitation to a dinner for the Bob-o-Links, a sorority-like group at school. According to Protti’s later testimony, she had planned to take Costas to the party to befriend her, but Costas became angry when she was told that there was no dinner for the new “Bobbies.“ The girls quarreled and Costas fled to the home of Alex and Mary Jane Arnold, telling them that her friend had gone “weird.“ When Costas could not reach her parents by telephone, Alex Arnold drove her home, noticing that the Protti family’s Pinto was following them. At the Costas home, Arnold, sitting in his car, saw Protti attack Costas. He thought that he was witnessing a fistfight, but in fact Protti had stabbed Costas five times with a butcher knife and fled. The Costases’ neighbors called an ambulance, but Kirsten was mortally wounded and died at a nearby hospital. Protti’s Arrest It took the police almost six months to find Costas’ killer. Protti passed a lie-detector test, but her alibi went unverified. After attempting to confirm Protti’s alibi, police suspected that she had lied. Following a conversation with an FBI agent who informed her that her arrest was imminent and that they knew that she had killed Kirsten, Protti wrote her mother a letter in which she made a full confession. Protti claimed to have found the kitchen knife by chance, and her elder sister, Virginia Varela, testified in court that she kept that knife in her car to cut vegetables. The Costases did not believe Protti’s story; they asserted that nobody would use an 18-inch-long (460 mm) butcher knife to slice tomatoes and that Protti, casually dressed that evening, never intended to take Kirsten to a party but had planned to murder her. Aftermath Protti was sentenced to a maximum of nine years, but was released seven years later in 1992 on parole at the age of 23. The Costas family left Orinda and moved to Hawaii in 1986. Costas’ parents vehemently opposed Protti’s release.