A 16-year-old boy accused of killing Brianna Ghey was a skilled kickboxer who “admired the craftsmanship” of the knife used to stab the transgender teenager, a court has heard. The boy, known as Y to protect his identity, told a jury that he saw his female co-defendant stab Brianna with his hunting knife in a Warrington park, denying that he was the only one strong enough to cut through her bone. Before killing Brianna, the girl was “giddy”, he claimed. Y gave evidence at his trial on Wednesday by typing his answers because he had been diagnosed with selective mutism disorder, a jury at Manchester crown court was told. Jurors previously watched interviews Y gave to the police after his arrest, in which he verbally blamed his friend, a 16-year-old girl known as X, for the “frenzied” stabbing in Culcheth Linear Park on 11 February. But the judge, Mrs Justice Yip, told the jury that since he was charged with murder he “gradually stopped speaking to anyone” apart from his mother and had been diagnosed with autism spectrum disorder, which affected the way he communicated, including volume and tone. It also affected his ability to make eye contact and how he “physically expresses himself”, Yip told jurors. She said his selective mutism was not a matter of choice, despite its title, and was beyond his personal control. Instead of going into the witness box – as Girl X did earlier in the week, when she blamed Y for the stabbing – Boy Y gave evidence over video link from a neighbouring room, and typed his answers for an intermediary to read out. He said he bought the hunting knife on a ski trip to Bulgaria six weeks before the killing, with “no ulterior motive” other than to “admire the craftsmanship”. He told the jury: “I like things made from metal and I like the way knives look.” After the killing, police found the knife in Y’s bedroom, with traces of Brianna’s blood and Y’s DNA – but no trace of X – the court heard. Y told the jury he gave the knife to X before they met Brianna on the day of the killing, adding: “I didn’t think she would try to seriously harm anyone.” He claimed he was urinating against a tree in the park when he heard a “puncturing sound” and turned around to see X stabbing Brianna “at least three times”. Cross-examining the boy, Girl X’s barrister, Richard Pratt KC, put it to Y that he was a “very good” kickboxer, but he replied that he was “only average”. Pratt asked the boy about evidence given by a pathologist who said “considerable force” must have been used to cut through Brianna’s bone and that “it needed some strength to do that”. The boy admitted he was stronger than Girl X and denied stabbing Brianna. Questioned by his barrister, Richard Littler KC, the boy described how he went over to Brianna and touched her body, getting blood on his hands, before X ran away and he followed her. Asked what they talked about after the stabbing, Boy Y typed: “Girl X told me to use my saliva to wipe the blood off my hands, as she was doing for her face. I had also asked her why she stabbed BG, she responded, ‘She tried to get me to break up with [her boyfriend] and that is unforgivable’.” Asked how he felt when he got home, Y said: “I wasn’t happy. I wouldn’t say sad either, from what I perceive sad as. I think that I was dazed by the event.” He did not tell his parents, he said. “I don’t tell them about easier topics, so it was even more improbable that I was able to tell them what I had seen … I assume it is linked to my autism and not being able to express myself clearly.” The jury has seen hundreds of text messages exchanged between the defendants. Boy Y said: “Girl X had a plan to stab BG but I did not.” He said he did not take her seriously “because she always talks about murder and nothing happens”. Boy Y began his evidence answering questions about his schooling, saying that he passed eight GCSEs after his arrest, and was now teaching himself A-level subjects including biology, chemistry, pure maths and English literature. He had hoped to study microbiology at university, the jury heard. The trial continues.