A man and woman who were arrested after the death of their 33-year-old daughter confessed they confined her to a tiny room for around 15 years due to a mental illness they say made her violent, police sources said Monday.

The police said that an autopsy showed the woman, Airi Kakimoto, whose body was recovered on Saturday from her Neyagawa home in western Japan's Osaka Prefecture, froze to death and that she was in a state of extreme malnutrition, weighing only 19 kilograms and standing 145 centimeters tall.

Outdoor surveillance cameras discovered at Osaka confinement site

Her 55-year-old father, Yasutaka Kakimoto, and 53-year-old mother, Yukari Kakimoto, reported her death to the police on Saturday and were arrested on the initial charge of illegally disposing of a body.

The woman is believed to have died around Dec. 18.

The police are now looking to build confinement and other charges after the couple admitted to investigators that they had held her in a room of around 3 square meters since she was 16 or 17 years old, the sources said.

The parents allegedly told police that recently they had only fed their daughter once a day.

According to the police, the Kakimotos renovated their house to add the small room fitted with a double door that can be unlocked only from the outside and a monitoring camera.

Inside the unheated room, there was a makeshift toilet and a tube designed to allow the woman to drink water from a tank sitting outside.