A 14-year-old girl and her 16-year-old boyfriend in Samut Prakan have admitted to planning the murder of the girl's mother in their flat in Bang Phli district on Thursday night, police said yesterday.
The girl claimed the motive behind the premeditated murder was her outrage over the mother's disapproval of her relationship with the boy and attempts to separate them.
The mother sustained multiple stab wounds after she was attacked by the boyfriend of the girl using a knife while she was sleeping in her bedroom, a police investigation found.
The girl's brother, Kitti, 23, sustained severe injuries as he attempted to save his mother.
Neighbours and security guards stopped the pair from fleeing the mother's apartment after the murder, and were then taken into police custody, the police said.
Chirapha, 53, the mother died at the scene. The brother was rushed to the hospital.
The boyfriend told the police he acted at the girl's request and it was the girl who prepared the knife and handed it to him before he began attacking the sleeping mother.
A police investigation also found that the pair, who are classmates at school, had been seeing each other for a long time yet kept their relationship secret from their families.
When the girl's mother found out she told the daughter to end the relationship, it made her hate the mother profoundly, according to the investigation.
The injured brother, however, said he and his mother never tried to ruin her relationship with the boyfriend as she claimed because they were not aware of their relationship until she ran away from home to be with the boy three days earlier.
He also dismissed his sister's claim that she possibly had a mental problem that might have led to the crime, saying she had no history of mental illness.
The boyfriend's father told the police his son brought the girl home three days earlier and claimed he got approval from the girl's family.
The girl's brother later came to pick her up and brought her home while the girl's mother at first threatened to pursue legal action against the boyfriend for allegedly depriving a minor of parental rights, said the father.
The girl's mother agreed not to take legal action when the boy's father promised to make his son stop seeing the girl, said the father.
He said his son had been treated for attention deficit hyperactivity disorder (ADHD) but had never been violent.