Prosecutors arrested five Nagoya Prison officials Friday in connection with the alleged mistreatment of a prisoner in September that led to his hospitalization.
Prosecutors also suspect other abuse in the penitentiary caused another inmate's death.
The five arrested were identified as Chief Warden Takashi Watanabe, 34, deputy chief wardens Akihiko Maeda, 40, and Hiromasa Okamoto, 46, and wardens Hiroki Ozawa, 27, and Hajime Ikeda, 30.
The five are suspected of attacking the 30-year-old male inmate on Sept. 25 when they placed him in solitary confinement because of unruly behavior, investigative sources said.