WARREN, Maine (AP) — A Maine State Prison inmate serving time for murder is facing a new murder charge for allegedly killing another prisoner last spring.

Maine State Police said 49-year-old Frank Higgins was charged Friday in connection with the beating death of 51-year-old Lloyd Millett. Millett was assaulted at the prison on May 24 and died June 7.

Higgins is serving a 45-year sentence in the 1999 stabbing death of his girlfriend, Katherine Poor, inside her apartment in Kenduskeag.

Millett was serving a life sentence after pleading guilty to strangling two women over a weekend in 1995 while he was working as a farmhand in Turner. Police found one of the victim’s bodies in a closet in his trailer, and the other in a field near a Lewiston hotel.