The Suffolk County Grand Jury yesterday returned indictments charging a Dorchester man with shooting two Maine residents in the head last summer, killing one and leaving the other near death, District Attorney Daniel F. Conley said today.

AMOS “ACE” DON (D.O.B. 3/11/86) is charged with first-degree murder for the Aug. 25, 2009, slaying of 29-year-old Erica Field; assault and battery with a dangerous weapon and armed assault with intent to murder for the shooting of Field’s boyfriend, now 32; and unlawful possession of a firearm for the handgun he allegedly used.

Field and the surviving victim, both from Lewiston, Maine, were shot inside a car in a Norwell Street truck storage lot. She died at the scene and he was left in critical condition, requiring several weeks of hospitalization.

Conley hailed the efforts of Suffolk prosecutors, Boston Police homicide detectives, and members of the Lewiston Police Department since the night of the homicide.

“Investigators here in Boston and in the victims’ hometown committed themselves to a thorough, exhaustive investigation,” Conley said. “A shared effort across jurisdictional lines brought us to this point, developing evidence strong enough to support our burden of proof.”

Prosecutors allege that Don and the surviving victim, accompanied by Field, travelled to Boston on Aug. 25 to obtain drugs for sale in the Lewiston area. Instead, Don allegedly directed them to the Dorchester lot and shot them both in the head.

“This case is about the assailant’s actions, not the victims’ choices in life,” Conley said. “No one deserves to be gunned down in cold blood and left to die in a parking lot far from home.”

If convicted of the murder charge, Don faces life in prison without the possibility of parole, Conley said.

Two months after the incident, Don was arrested on an unrelated federal gun charge. He has since pleaded guilty to that offense and awaits sentencing in the U.S. District Court for Maine. His arraignment on the Boston charges, at which additional details are expected to emerge, has not yet been scheduled.

Assistant District Attorney Ian Polumbaum led the grand jury investigation that led to yesterday’s indictments. Paula Connor is the victim-witness advocate assigned to the case. Attorney Stephen Weymouth has been appointed to represent Don.