A mother and her boyfriend in Sapporo were referred to prosecutors Friday on suspicion of assaulting her 2-year-old daughter, who was pronounced dead at a hospital Wednesday.

The suspected abuse of Kotori Ikeda occurred despite a child welfare official interviewing her mother last year following a tip and a police officer meeting with the mother and the girl in mid-May, according to investigative sources.

Rina Ikeda, 21, and her boyfriend, Kazuya Fujiwara, 24, are suspected of assaulting Kotori between early May and Wednesday at Ikeda's home and other locations, local police have said.