Police Tuesday arrested and began questioning a 25-year-old man on suspicion of beating to death his girlfriend's 4-year-old son, according to police.
Yuji Takahashi, a company employee from Yokohama, was arrested on suspicion of kicking Nao Miyashita, the third son of 31-year-old Akiko Miyashita, in the stomach and punching him several times in the face at around 11 p.m. Monday, resulting in the child's death.
Police said Takahashi, who works at an insurance company with Miyashita and had been dating her since April, told them that he beat the boy because the victim did not like him and had behaved badly after dinner.
An autopsy to determine the cause of death was slated for later Tuesday, police said.
The boy was pronounced dead at a Machida hospital late Monday after his mother called an ambulance, police said.
Miyashita reportedly told paramedics that the boy fell unconscious after fighting with his two brothers, aged 9 and 7. But the two boys have told police there was no fight.
Police said Nao's nursery school had reported to the Machida Municipal Government on May 17 that the boy had scars and bruises on his face.