A Thomaston man charged with manslaughter in the shooting death of his fiancee during a prospective gun sale in the parking lot of a Bath supermarket last fall will plead guilty to a lesser charge, his attorney said.

Dylan Grubbs, 23, will enter a guilty plea at 10 a.m. Monday in Sagadahoc County Superior Court in West Bath, said his attorney, David Paris, by phone Thursday night. Paris would not specify what charge Grubbs would plead to in an agreement with prosecutors.

Grubbs, who is being held in the Two Bridges Regional Jail in Wiscasset, was charged with manslaughter in the fatal shooting of Chelsea Jones, 22, of Thomaston in the parking lot of the Shaw’s supermarket off Route 1 on Nov. 16, 2015.

The case is being prosecuted by Assistant Attorney General Leane Zainea and Jonathan Liberman, deputy district attorney for Sagadahoc County.

Liberman, reached by phone Thursday afternoon, said it is his office’s policy to not comment on matters that are pending in court.

“Out of respect for the (Jones) family, I am not going into any further detail until the matter has been resolved in court,” Paris said when asked what the lesser charge would be.

In Maine, criminal homicides fall under three categories: murder, felony murder and manslaughter. A person is guilty of manslaughter if they recklessly, or with criminal negligence, cause the death of another human being.

Grubbs and Jones were parked outside the supermarket in Bath when he got out of the vehicle to show a 9 mm Taurus pistol to a prospective buyer. Jones was sitting in the front seat of their SUV and was shot in the head when the gun went off. She died three days later at Maine Medical Center.

State police initially described the shooting as accidental, but Grubbs was indicted by a Sagadahoc County grand jury in February.

In March, Grubbs was arrested on a charge of driving under the influence of drugs. He was charged with three counts of unlawful possession of scheduled drugs, operating under the influence, and violating his conditions of release, according to the VillageSoup online newspaper.

Jones and Grubb had two children, Kyleigh and Jordan Grubbs of Thomaston. The children have been living with their grandparents, Paris said.