GWINNETT COUNTY, Ga. -- A 17-year-old showed no emotion as police laid out details of the grisly killings of her grandparents Wednesday.

Cassandra Bjorge and her 19-year-old boyfriend Johnny Rider have been charged with murder and aggravated assault in the deaths of Randall and Wendy Bjorge, both 63 years old. The victims were found with their throats slit on April 8. Police believe they had been dead for about a week before their bodies were found.

In a preliminary court hearing on Wednesday, police said that Cassandra Bjorge confessed to stabbing her grandparents. Authorities also said she and her boyfriend partied in the house the week after the killing, caulking the doors and windows to conceal the smell of the bodies.

Bjorge and Rider were officially charged with the murders when they were released from the hospital after what police believed to be a suicide attempt.

Check back later for more details of the preliminary hearing.

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Police have called this a "very unique and disturbing case on so many levels," and said they may not ever find a scenario that makes sense to a "reasonable person."

According to police records, Cassandra Bjorge had previous run-ins with violent behavior. When she was 16, she was charged with assaulting her grandmother. Police had also been called to the residence several times in the past after the teen ran away.

Her boyfriend, Rider, had already been charged for allegedly beating his sister with a baseball bat and pepper spraying her while in possession of the Bjorges' car.

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