HIROSHIMA (Kyodo) Four staff members at a Hiroshima Prefecture reformatory are under arrest for allegedly assaulting minors at the institution in what prosecutors call a widespread series of abuses.

An internal probe found that the four and others among the 35-member staff assaulted almost half of the 100 minors at the institution in 2008 alone.

Katsunori Tahara, 43, Daisuke Matsumoto, 29, Katsuya Nobata, 32, and Akira Sugawara, 26, are suspected of assaulting four of their charges aged 16 and 17 between March 2008 and March this year.

Tahara, senior to the other three, allegedly choked a 17-year-old with his hands after pinning him down and telling him to die.

The allegations include preventing the minors from using the bathroom, and spraying water on their pants and forcing them to wear diapers.

The case came to light in April after one of the minors told a staff member at the reformatory he had been subjected to violence by staff, prompting a branch of the Justice Ministry to conduct an internal investigation.

"I think people are increasingly losing the sense that the reformatory is meant for protecting and correcting minors instead of punishing them like in prison," said Koichi Kikuta, a legal expert and professor emeritus at Meiji University in Tokyo.