The 16-year-old girl accused of murdering Brianna Ghey carved her boyfriend’s name into her own arm and once claimed to be a satanist, a jury has heard. Her co-defendant, a 16-year-old boy known as Y to protect his identity, told police he saw the girl, known as X, stabbing Brianna in Culcheth Linear Park, in Warrington, on 11 February, Manchester crown court heard. In a police video interview played to the jury on Monday, the boy said the girl was “not a normal person” and she used to “joke about dead babies”. He said: “I know she has been diagnosed with bipolar disorder. She has had a history of drug use and alcohol abuse.” Asked if X “carries knives”, Y said: “No, but I know that she uses knives, she carved her boyfriend’s name into her arm and it’s still scarred on to her arm.” She was “obsessed” with her boyfriend, he claimed, and used to self-harm. The court has previously heard Brianna was stabbed 28 times and that her blood and Y’s DNA were found on a hunting knife belonging to Y. He told police he bought a hunting knife on a ski trip to Bulgaria, and drew a picture of it. Y said X told him she had killed two people, but added: “I’m not sure if it’s true because there’s no news about it.” The prosecutor, Deanna Heer KC, has previously told the jury there is no evidence X is responsible for any other killings. The boy said the girl told him she liked watching torture videos and “in Year 8 she was saying she was a satanist”. He said: “She would joke about it: ‘I’ll stab your nan, shag your cat’.” In his interview, Y said he was urinating against a tree when he turned around to see X stabbing Brianna. Afterwards, he said he asked X why she had done it. “She was saying how Brianna tried to break her and her boyfriend up,” the boy told police. Asked for his reaction to the news Brianna had died, Y said: “I felt like my heart stopped, just, I didn’t know how to react.” Y claimed X stopped stabbing Brianna because she had “seen somebody”. Asked if X had ever said she had “any sort of ill feeling” towards Brianna, Y said: “I’m not sure, she doesn’t like lots of people.” In her police interview, also played to the jury on Monday, X said Y was “a weird kid” and that they were “frenemies” before they became friends, a court heard. She told detectives: “We was kind of like frenemies. We was like friends and both kind of like didn’t like each other that much at the same time.” X said she and Brianna had been friends for a few months before she was killed, after Brianna complimented her on her eyeliner. She said she knew Brianna was trans before they became friends, and that “people used to make fun of her for being trans”. She claimed Brianna had been suspended from school at the time of her killing, after an argument with a teacher, and that she was bullied. She also said Brianna suffered from anxiety and self-harmed. She described how she and Y met Brianna off the bus by Culcheth library on the day of the killing. She said she and Y were “hanging out” with Brianna in the park when Brianna “ditched” them to meet “a lad from Manchester”. She said Brianna was wearing her hood up at the time because she was self-conscious about her hair extensions, which she “hadn’t attached properly” and so the clips were showing. Both children were softly spoken and calm in their police interviews, each accompanied by a solicitor and a relative acting as an “appropriate adult”. Before the videos were played to the jury, the judge reminded them that Y had been diagnosed with autism, ADHD and anxiety; and that X had “traits of autism” and anxiety. Mrs Justice Yip told the jury to “guard against making assumptions based on the presentation” of the defendants during their police interviews. She added: “Be careful not to be unfairly influenced by body language or appearance … That’s particularly important when you are assessing the reactions of someone that might not be the same as someone you may describe as neurotypical.” Each defendant denies murder and accuses the other of the killing. The trial continues.