The teen appeared in court with slashes on her face, imitating The Joker. She made the cuts herself to plead insanity when she was caught, she said.
An English schoolgirl obsessed with serial killers appeared in court with slashes on her face before she was found guilty of the attempted murder of her best friend.
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"It seems that she decided to kill her best friend," said Judge James Newton-Price QC. "She had already researched online how to kill swiftly and effectively with a knife.”
The teen, who has not been named, appeared in court for the stabbing of her classmate with two slashes on each side of her mouth extending to her cheeks.
According to court documents, she told the jury she wanted to look like Heath Ledger's Joker character in The Dark Knight, The Guardian reported.
She also told the jury she made the cuts herself so she could plead insanity when she were arrested.
The teen, a student of the Petersfield School in Hampshire, however, covered up the fresh slashes on the day of the April 2015 attack.
She reportedly pulled her best friend aside at school, and told her to "close your eyes and put your hands out," as she offered her a present.
Her friend, 15, opened her eyes just in time to spot the weapon, and jump away.
The knife, which the perpetrator pulled out of a bag as her friend had her eyes closed, had pierced her school uniform blazer and shirt, but left the victim with only a superficial puncture wound.
According to the BBC, the teen bore a grudge against the victim because she set up fake Instagram and Twitter accounts in her name
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The teen later messaged her victim, saying the Joker and Columbine "motivated" her actions.
"The defendant was for a period of time obsessed with serial killers and school shootings and the notoriety that attaches to those who commit those crimes," Newton-Price said.
Other killers she revered included U.S. serial killers Ted Bundy and "Night Stalker" Richard Ramirez, along with Norway's Anders Breivik.
According to court documents, she also kept a "kill list" of her potential victims that was later burned, which included other students at her school, and her mother and brother, whose throat she planned to slit while she slept.
While she has pleaded guilty to having a bladed weapon on school premises and unlawful wounding, she later told the jury: "I didn't feel very much in control of what I was doing. I didn't want to, I felt I had to, I felt that within myself. A very big part of me was disgusted at what I was thinking."
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The teen ultimately denied wanting to kill her victim, but admitted wanting to harm her.
She was led out of the courtroom in tears.
The judge ordered her to undergo a psychiatric exam before her sentencing in a few weeks.
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