A former federal correctional officer pleaded guilty in U.S. District Court Monday to sexually assaulting a female inmate at the Federal Detention Center in Hono­lulu.

Richard Seaman, 47, faces a maximum 15-year prison term at sentencing in April.

He pleaded guilty to one of five counts of sexual abuse of a ward. Seaman said he was working as the commissary supervisor on Dec. 8 last year when he had sex with the inmate.

Federal prosecutor William Shipley said Seaman had sex with the inmate in the commissary or a storage room behind a closed door. The woman saved DNA on her shirt from the encounter and turned the shirt over to investigators. Shipley said the DNA from the shirt matches Seaman’s DNA.

In exchange for the guilty plea, the government promised to drop four other charges accusing Seaman of sexually assaulting the same inmate in September, October and November of 2011.