A girl accused of the “frenzied” murder of transgender teenager Brianna Ghey told a jury she heard a scream and turned round to see her co-accused stabbing her.

The 16-year-old, identified only as girl X, became visibly upset as she told the jury she saw another teenager, identified only as boy Y, knifing Brianna.

Brianna was stabbed 28 times in her head, neck, chest and back with a hunting knife after, prosecutors allege, she was lured to Linear Park in Culcheth, near Warrington, on the afternoon of February 11 earlier this year.

Both girl X and boy Y, aged 15 at the time – now both 16, deny murder and are blaming each other for Brianna’s death. Neither can be named due to their age.

Jury members at Manchester Crown Court have seen an alleged handwritten “murder plan” found in girl X’s bedroom and been shown text messages between her and boy Y, allegedly showing the plan to lure Brianna to the park and kill her.

Girl X, sitting in the witness box beside an intermediary to look after her welfare, wiped away a tear as she denied murder and said any talk of harming Brianna was just “a fantasy”.

She said she expected herself, boy Y and Brianna were just going to “hang out” in the park that Saturday afternoon and they stopped near a bench.

Girl X said she then got a bit bored and walked away from the bench to stretch her legs.

Richard Pratt KC, defending girl X, said: “Did something attract your attention?”

Girl X replied: “Yeah. When I walked off, I heard a noise like someone screaming and that’s when I turned around.”

Mr Pratt said: “What did you see when you turned around?”

Girl X replied: “I saw boy Y stabbing Brianna.”

She indicated on a photo of the crime scene that this was happening on the path a short distance from the bench.

Mr Pratt asked: “How many times did you see boy Y stabbing Brianna?”

Girl X replied: “Around five times. I saw her fall and land face down on the floor. I saw him stood next to her, leaning over, looking down at her.”

Mr Pratt continued: “How did this make you feel?”

Girl X said: “I was in shock.”

Mr Pratt said: “Did you expect that was going to happen? Did you want it to happen?”

“No,” girl X replied.

Earlier, girl X admitted watching internet torture and killing material from the “dark web”, and having an interest in serial killers.

She also admitted she had “dark fantasies” of killing other children, including of killing Brianna – but had no intention of making any of it reality.

I knew if I tried to step in boy Y could easily have overpowered me in that situation

Mr Pratt continued: “You told the jury of your interest in films. Did you like seeing Brianna stabbed in that way?”

“No,” girl X replied.

Mr Pratt said: “What did you do?”

Girl X replied: “I knew if I tried to step in boy Y could easily have overpowered me in that situation.”

She denied taking part in the stabbing or telling boy Y to stab Brianna.

Girl X added: “I walked over to see whether I could see her breathing. I couldn’t.”

She said boy Y ran off and she “panicked” and ran with him.

I was scared if I tried to ask him (what happened) he could come after me thinking I could snitch

She said she did not ask boy Y about what had happened because she was “in shock”.

She added: “I was scared if I tried to ask him he could come after me thinking I could snitch.”

Judge Mrs Justice Yip asked girl X if she was alright as she appeared to wipe tears away with the sleeves of her cardigan, before being handed a tissue by her intermediary.

The court heard that the following day girl X told her mother, and then the police, that Brianna had been with her but left to meet someone from Manchester.

Asked why she did not tell the truth, girl X said: “I was scared because obviously I knew how bad it would look, just based off of text messages, so I was defending myself as well as boy Y at the time.”

She said she sent messages via Snapchat to Brianna after her death because she started to get “really paranoid”.

Finishing his questioning, Mr Pratt asked girl X how she felt about the fact Brianna had died.

She replied: “I do feel really upset about it.”

Girl X confirmed a crumpled, handwritten note of an alleged “murder plan” to kill Brianna found on her bedroom floor by police, had been written by her.

But she said it was another fantasy and not a real plan to carry out a killing.

Notes were also made on serial killers including Jeffrey Dahmer, Richard Ramirez and Harold Shipman in a black Pukka notebook.

Jurors have heard X and Y had a fixation with torture, violence and death, with girl X describing herself as a “satanist”.

Richard Littler KC, defending boy Y, who denies he attacked Brianna and claims he saw girl X doing the stabbing, then questioned the witness.

He pointed out girl X told Brianna to buy a single ticket, not a return ticket, when she travelled to meet the defendants on the day she died.

And he said boy Y had never met Brianna before that day.

Mr Littler said: “It was your idea to kill Brianna. It was your idea to stab her.”

Girl X replied: “There was no intent.”

Mr Littler said: “Put aside intent. It was your idea?”

“Yeah,” girl X replied.

Girl X also admitted she had “lured” Brianna to the park and admitted lying to her mother, boyfriend and police about what had happened in the park.

Mr Littler cited a notebook found at girl X’s house of her describing boy Y as, “very, very smart, genius level” but also a “sociopath”, lacking emotion and socially awkward, who only had three followers on Instagram.

Girl X denied the suggestion she tried to control or manipulate boy Y.

Mr Littler continued: “He did not have many friends did he? But he had you as a friend?”

Girl X replied: “Yes.”

The trial was adjourned until Tuesday morning.