A prison guard fatally shot his estranged girlfriend, then turned the gun on himself while both were on duty at a women's prison, authorities said.

Daniel Bunton, 35, and Stacey Davis, 31, died in the murder-suicide Sunday at Chillicothe Correctional Center, said Livingston County Coroner J. Scott Lindley.

The couple had been living together but recently separated, authorities said.

Bunton and Davis passed each other in a hallway Sunday afternoon and "exchanged words," Lindley said. A senior officer told Davis to leave the area and finish her duties.

Moments later, she was shot.

"He shot her as she was going out the door," Lindley said. "He shot her from behind and then he took his own life."

Several people witnessed the shooting, which happened outside a building that houses a library and classroom, authorities said.

Prison guards at the 525-bed prison are not allowed to carry guns for their jobs. While there are occasionally random searches, guards do not have to pass through metal detectors, said prison Superintendent Jennifer Miller.

Investigators were interviewing about 20 witnesses, corrections spokesman Brian Hauswirth said.