Five of the six Nagoya Prison guards charged with killing one inmate and injuring another by abusing a restraining device last year pleaded not guilty Tuesday. The sixth partially owned up to the charges.

On the opening day of their trial before the Nagoya District Court, Deputy Chief Guard Akihiko Maeda, 41, guard Hiroki Ozawa, 27, and three others entered the not guilty pleas to charges of physically abusing two inmates by using a leather belt with manacles.

Deputy Chief Guard Hiromasa Okamoto, 47, charged with severely injuring an inmate in September, accepted responsibility for improperly using the restraining device.

"It was not for the purpose of punishment," Okamoto said. "But the use (of the device) was beyond the scope of occupational limits, and I accept responsibility."