TOKYO (Reuters) - Japanese police said on Wednesday they have arrested a couple whose 33-year-old daughter froze to death in a tiny room where they had confined her for years because they believed she had a form of mental illness that made her violent.

Western Japan’s Osaka Prefectural Police Department said Airi Kakimoto’s body was found in a state of extreme malnutrition after her parents reported the death on Saturday. She was 145 cm (4.76 ft) tall and weighed just 19 kg (42 lb).

Police said Yasutaka Kakimoto, 55, and Yukari Kakimoto, 53, had confessed that they fed their daughter only once a day and kept her in a 3-square-metre room for some 15 years.

“Our daughter was mentally ill and, from age 16 or 17, she became violent, so we kept her inside the room,” police quoted her parents as saying.

People with mental and physical disabilities and their families can still suffer stigma and shame in Japan despite some changes in public attitudes.

Police said the parents added the small room - fitted with a camera and a double door that could only be unlocked from the outside - to their house and equipped it with a makeshift toilet and tube to a water tank outside.

About 10 surveillance cameras were installed outside the single-storey home, which was surrounded by a 2-metre high fence, police said.

The parents found their daughter dead on Dec. 18 but they reported the death Saturday. “We wanted to be together with our daughter,” police quoted them as saying.

Police said the couple were arrested on suspicion of illegally disposing of a body, a step that often precedes more serious charges.