WARREN, Maine — A Maine State Prison inmate serving a life sentence for murder has died after being attacked by another inmate who is in prison for murder. State police say 57-year-old Alan Powell died at about 6:30 p.m. Tuesday after being attacked by Guy Hunnewell, 42, in an exercise area of the Maine State Prison in Warren. Spokesman Steve McCausland said that detectives have interviewed guards and inmates and that the case will probably be presented to a grand jury in July. Hunnewell is serving a 40-year sentence for fatally stabbing his girlfriend in a jealous rage in 1997. Powell was convicted of sexually assaulting, stabbing, and strangling 65-year-old Martha Daigle, the mother of 17 grown children, in her Waterville apartment in 1989. Her body was found by her 12-year-old grandson.