Tokyo (CNN) A couple in Japan have been arrested after their emaciated adult daughter was found dead in a windowless room where she had apparently been locked for at least 15 years.

Airi Kakimoto, 33, weighed less than 20 kilograms (42 pounds) -- about the average weight of a 4-year-old -- when her body was discovered Saturday, police said. She appeared to have died from exposure to the cold.

Yasutaka Kakimoto, 55, and Yukari Kakimoto, 53, who live in Osaka, in central Japan, kept their daughter in an unheated structure next to their house, according to police.

They had the room made and fitted with surveillance cameras, an air conditioner and a toilet, and had kept their daughter locked up from the age of 16, her father told police.

They fed her one meal a day and forced her to drink water through a tube.

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