Police served fresh arrest warrants on a woman and her live-in partner Thursday for allegedly killing the woman's sick 5-year-old son, police said.
Yumi Kato, 26, and Naoki Itagaki, 30, were previously indicted on charges of dumping the boy's body on a mountain in Yamagata Prefecture.
The pair are suspected of leaving Kato's son, Sho, to die June 17 after Itagaki repeatedly assaulted the sick boy, the officials said.