A-Level student was bitten on the thumb by boyfriend she then stabbed - court hears
Katherine McGrath, aged 19, denies killing Alyn Thomas, from Cymmer, near Port Talbot, at her home in Bridgend after a drinking session on the day she received her A-level exam results.
Police interviews played at Cardiff Crown Court heard her say she was trying to stop Mr Thomas attacking her.
The court also heard that Miss McGrath had been a good pupil at school.
In the police interviews, Miss McGrath described the moments leading up to her using a steak knife to stab Mr Thomas.
"I said please, please go back. Please stop what you are doing, you are hurting me," she said.
"He had already pushed me and spat on me. I didn't know what he could have done next. I had no idea what he was capable of."
Miss McGrath, described as a top pupil at Brynteg Comprehensive School in Bridgend, chose not to give evidence at the murder trial.
A statement from her former head of sixth form, Stephen Rudall, said: "As a pupil there were never any issues and she was a form representative for years 12 and 13.
"She had a good attendance and attitude and there were never any issues surrounding her behaviour.
"She was above average academically. I was extremely shocked when I heard about her arrest because she was such a pleasant student."
The court has heard Mr Thomas had two previous convictions for assault after fighting in a nightclub.
Mr Thomas died after being stabbed at the McGrath family home
Miss McGrath claims her boyfriend bit her on her thumb during an argument at her family's home in Brackla, Bridgend.
The wound was examined by a forensic dentist who confirmed it was caused by Mr Thomas.
Forensic dentistry expert Kathryn Adams said: "Marks on McGrath's right had are the result of a bite of considerable force from Alyn Thomas's incisor teeth.
"Kathryn McGrath's right thumb was painful, swollen, and had obvious redness up to the joint.
"It was typical of a human bite injury when teeth have penetrated through the skin.
"A bite of this type would have been extremely painful when it was inflicted."
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