AUGUSTA – An Augusta man fatally beat and stabbed his 74-year-old mother-in-law after an argument over the proper way to start a snow blower, a prosecutor said.

After killing the woman, David Grant drove around with Janet Hagerthy’s body in his pickup truck before he dumped her body near her Farmingdale home, Assistant Attorney General Andrew Benson told jurors Monday in Kennebec County Superior Court.

Defense lawyer Christopher MacLean said no one disputes that Grant killed Hagerthy. But he said the self-employed carpenter was suffering from severe psychosis caused by heavy drug use that included cocaine and crystal methamphetamine.

“He never had a trace of motive or premeditation in his mind when he went to Janet Hagerthy’s house,” MacLean said. “This was a sudden, unexpected, unplanned, unpremeditated, irrational act that had no logical explanation whatsoever.”

The trial continued Tuesday.

Hagerthy, a retired nurse, was killed on Nov. 30, 2004. Hagerthy’s body was found a few streets away the next morning.

The cause of death was multiple injuries to the head, face, neck and torso, said Dr. Margaret Greenwald, Maine’s chief medical examiner. A stab wound to the right side of her neck was the most serious wound, she said.

Grant, 56, was found in his pickup truck in a ditch near the Newport exit of Interstate 95 about 10 hours after the killing. Police who testified Monday said they found him repeatedly stabbing himself in the neck with a knife.

MacLean said Grant was suffering from severe psychotic episodes during the entire month of November 2004. More than once, MacLean said, Grant called police about children allegedly running on his roof and peeping in his windows.

“Police were so concerned that they made him go down to the emergency room and get checked out,” MacLean said.

Hagerthy’s daughter, Cynthia, testified Monday that Grant’s drug abuse caused their relationship to degenerate and that she had contemplated divorce or separation even before her mother’s death.

She said she had planned to have dinner with her mother the night she was murdered. She has since divorced Grant.