Photo/IllutrationThe Sanda Police Station in Hyogo Prefecture (The Asahi Shimbun)

SANDA, Hyogo Prefecture--An elderly man here was arrested after city authorities alerted police that he had kept his 42-year-old son confined in a wooden cage at home possibly for the past two decades.

Hyogo prefectural police said Yoshitane Yamasaki, 73, was arrested April 7.

The son, who has a psychiatric disability, has been cared for by a social welfare facility since January after Sanda municipal authorities looked into the matter.

The son did not have any obvious health problems, but city officials concluded he had been abused.

City officials visited the Yamasaki residence in January and discovered the son in a cage in a prefabricated facility next to the main house.

The father told city officials the cage was installed after his son started becoming violent at home.

Investigative sources said the son may have been kept confined for more than 20 years.

The cage was just large enough to allow an adult to lie down and could be locked.

In a similar case in Neyagawa, Osaka Prefecture, a woman with a psychiatric disability was found dead in a tiny chamber next to the family home in December 2017. Her parents have since been indicted on charges of confinement and abandoning their responsibility to care for the sick child and causing her death.