WALPOLE, Mass. (AP) – An inmate serving time for assaulting prison guards in 1997 managed to open his cell door and used a makeshift weapon to wound two guards at the maximum security Cedar Junction state prison, a Massachusetts Department of Correction spokeswoman said Sunday.

The male guards subdued the inmate despite suffering cuts in Saturday night’s confrontation, department spokeswoman Diane Wiffin said.

The most seriously injured guard suffered facial wounds, and remained hospitalized Sunday, Wiffin said. The other guard was treated at a hospital and released.

The inmate somehow managed to open the door of his cell in the prison’s disciplinary unit, leading to the confrontation with the guards, Wiffin said.

Afterward, the inmate was returned to another cell. He was not injured.

Prison staff were investigating how the cell door was opened, and were inspecting all 120 doors in the prison’s disciplinary unit as a precaution, Wiffin said.

The Norfolk County District Attorney’s office was investigating.

Wiffin declined to identify the wounded guards or the inmate, and she did not say where the guard who remained hospitalized was being treated.

Wiffin said the inmate was convicted of armed robbery in 1988 and sentenced to nine years to 10 years. In 1997, he was ordered to serve another 36 years to 40 years in prison for assaulting two corrections officers at Cedar Junction.