PORTLAND – A Casco man facing an upgraded charge of murder in the shooting of his girlfriend pleaded innocent at his arraignment in Cumberland County Superior Court on Tuesday.

Gary Sweeney, 45, initially was charged with manslaughter in the death of Christine Pepin after he was arrested Feb. 4.

Police found Pepin dead with a gunshot wound to the head. Sweeney told detectives that he shot her but did not know the gun was loaded, according to the police.

A Cumberland County grand jury determined the crime was committed intentionally and upgraded the charge to murder.

Manslaughter convictions are punishable by up to 40 years in prison, with sentences in excess of 20 years reserved for the most heinous and violent cases. The penalty for murder is between 25 years and life.

The shooting occurred after Sweeney, Pepin and their 11-year-old son, Jesse, returned from a neighbor’s home after dinner and drinks, according to the police and witnesses.

Jesse Sweeney told police that his parents seemed drunk before the shooting. He said he stayed outside to play in the snow until his father appeared in the doorway and yelled at him. Sweeney brought a small-caliber revolver to the door, held it in the air and pulled the trigger nine times, but it made only clicking noises, Jesse Sweeney said.

The boy said he heard his father ask his mother where the bullets were and then heard his mother telling Sweeney to “get off of me now!” Frightened, the boy ran to the neighbor’s house for help.