A 15-year-old Danish girl has been sentenced to nine years in prison for stabbing her own mother after becoming obsessed with videos depicting brutal beheadings carried out by the Islamic State group.

The court heard how Lisa Borch and her 29-year-old Iraqi boyfriend had watched video of British hostages David Haines and Alan Henning being killed by Islamic State militants for hours before stabbing her mother, Tina Römer Holtegaard, at her home in rural Kvissel.

Borch alerted authorities to the incident, telling them she saw a “white man” running from the house, but when police arrived at the house she didn’t look up from her computer and simply pointed upstairs to the scene of the crime.

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She reportedly met boyfriend Bakhtiar Mohammed Abdullah at a refugee center near her home, after ending a relationship with another older Muslim man.

Borch’s twin sister told the court that Lisa had moved out after “endless rowing” with her mother over her relationship with Abdullah. The two had planned to flee Denmark after the stabbing to join Islamic State militants fighting in Syria.

Jens Holtegaard, Borch’s stepfather, told the UK Telegraph that he was worried Borch would become further radicalized during her time in prison.

“Lisa is completely uncritically enthusiastic about everything related to the immigrant community. She loves to talk about ISIS and their brutal behavior in the Middle East,” he said. “I dare not imagine what she can develop into during imprisonment.”