The bodies of four infants were found Saturday in a cardboard box left on the second floor of an apartment building in Fujimi, Saitama Prefecture, police said.
The bodies were found in the apartment of Takako Kanekawa, 53, who was found dead there by her boss on Wednesday, the police said.
Kanekawa's 44-year-old sister made the gruesome discovery at around 10:30 a.m. while cleaning the room.
The police said the four bodies were in a plastic container that was in a black plastic bag, and that the bag was put in a cardboard box and left in a closet in the living room.
The bodies appeared to be those of newborns, but were unable to be identified further because they had decomposed so much. Three of the corpses were 47 cm to 48 cm tall, the police said.
Kanekawa, who had lived alone in the apartment since August 1996, was discovered after her boss came to check on her because she had failed to come to work since the beginning of this month. It appears she died after spitting up blood, and the police believe she died of an illness.