Prosecutors have arrested a guard and an inmate at Osaka Prison on suspicion the inmate tried to improve his treatment in the prison, officials said.

Guard Yoshimi Kohata, 32, is suspected of receiving 300,000 yen in cash in Tennoji Ward, Osaka, around May 12 from an acquaintance of Hirohito Nakajima, 32, who is in prison on a separate bribery conviction.

Both have reportedly admitted to the allegations.

The prosecutors say Kohata took the money knowing it was in exchange for giving Nakajima preferential treatment.

Suspicion that bribery was taking placed surfaced through a letter to the justice minister written by another inmate in Osaka Prison.

Kohata, who was hired by the prison in 1997, has been in charge of a physical labor area.

In a similar case, a chief guard at the Osaka Detention Center got a suspended sentence in February for receiving gifts in return for special treatment of incarcerated gangster and union leaders. He has been fired.