An 18-year-old high school student here was arrested Tuesday on suspicion of beating the 4-year-old son of his girlfriend to death, local police said.
The child's 27-year-old mother, Aya Morishima, was also arrested for allegedly harboring a criminal.
According to investigations, the teen attacked Morishima's son, Yuki, at her home in Nagoya's Showa Ward at around 7 a.m. Tuesday. The attack allegedly included kicks to the abdomen. The child later died of hemorrhagic shock.
The mother meanwhile allegedly tried to protect her boyfriend by telling them that Yuki had injured himself in a fall.
The pair were at the house when ambulance personnel arrived in the afternoon. Police are questioning them because Morishima's account of the incident was inconsistent.
Staff at the nursery school Yuki attended noticed in July that the boy had bruises on his face and back. He was also injured in August, and school officials notified the local child welfare office the following month.
On Oct. 7, welfare officials informed police at Showa Police Station that they suspected the mother's boyfriend abused the child on a regular basis. Police responded by urging them to get the mother to file a report.