A 65-year-old man and his 28-year-old stepdaughter have been on suspicion of killing their baby boy by cutting its neck immediately after birth, police said.
Eishi Nakamura, a part-time worker, and Kazumi Nakamura, the daughter of a woman he married, allegedly killed their newborn baby at their home in Itoigawa, Niigata Prefecture, around summer 2014, according to the police.
The man is also suspected of dumping the baby's body.
The police said he has denied all of the allegations after he was arrested Monday.
They suspect he instructed his stepdaughter to kill the newborn.
The police said they learned of the case after Kazumi Nakamura, persuaded by a friend, turned herself in to the police after moving to Handa, Aichi Prefecture, in February.
The police have confiscated a knife they believe was used for the murder, but they have not found the baby's body.