GRINDSTONE, Pa. -- A Fayette County man who police said was fighting with his live-in girlfriend has been charged with fatally shooting his 12-year-old son during the argument.

Michael Alvin Muha, 39, shot his son, also Michael Alvin Muha, in the chest on Sunday night, state police said. He faces charges of criminal homicide, aggravated assault and reckless endangerment, but police said it appears the shooting was accidental.

Muha's girlfriend, Tasha Miciotto, was also wounded during the argument at their home in Redstone Township. She is expected to be released from a Pittsburgh hospital on Monday, state police Trooper Joseph Christy said.

Muha told police he asked his son to get a shotgun from his car during the argument with Miciotto, according to an affidavit filed with District Justice Jesse Cramer. Muha told police he loaded the gun with two rounds and it later discharged, striking his son in the chest, the affidavit said.

"It doesn't appear that the young man was in an altercation with his father, so he may have been a victim of the gun discharging and him not being the intended target," Christy said.

Miciotto told police she had been arguing with Muha when the boy came into the house with the gun. Miciotto said Muha began waving the gun around, the affidavit said.

She told police she turned to run when the gun went off. She was struck in the eye, and told police when she turned around she saw the boy lying on the floor, already dead.

However, Jean Shaw, Michael's grandmother, told Channel 11 News that another child in the house at the time of the incident claims Miciotto allegedly had control of the shotgun during a struggle for the weapon.

"She had a hold of the trigger, and the gun came back down, and that's when (Miciotto) pulled the trigger, and it hit Mikey," Shaw said.

A neighbor, Wesley Joseph Silva, told police he heard the elder Muha yell that "he was going to shoot somebody because he wasn't going to have this problem anymore," according to the affidavit.

Silva told police he heard a gun go off, then someone scream, "He's dead!" Silva called 911 after hearing the gunshot.

Another neighbor, Valencia Barnes, said the family was close-knit.

"Mikey was a good boy, well-mannered, had a lot of things going on in his life," Barnes said about the younger Muha.