WILLIAMSTOWN — Gina Anne Murphy told state police she was defending herself from her knife-wielding ex-husband when she retrieved her .22-caliber revolver and fatally shot him in the chest Monday night.

It was the latest in an ongoing pattern of threats from her ex-husband, she told investigators. Murphy has not been charged in Dauphin County’s ninth homicide of 2012, but some midstate criminal defense attorneys said Thursday she might have a difficult time arguing self-defense.

What it might come down to is the gap of time between the threat with the knife and when she retrieved her weapon, said Harrisburg attorney Brian W. Perry of Gover, Perry & Shore.

“If it happened simultaneously, that’s one thing,” Perry said. “If he threatened her with a knife and she was able to get out of the situation, go into another room, grab her gun and comes back and shoots him, that’s going to be hard for her self-defense claim.”

A grand jury will meet Friday to determine if charges will be filed against Murphy, said Trooper Adam Reed, a state police spokesman. The fact-finding effort will likely take several days, Reed said.

Daniel Joseph Murphy, 52, died of a single gunshot wound to the heart after he was shot about 10:45 p.m. at the Murphys’ home in the 400 block of East Market Street. When troopers arrived, they found Gina Murphy kneeling over her ex-husband’s body, according to court papers.

Despite being remarried to others, the Murphys were living together in the two-story, stone house surrounded by a white picket fence in the northernmost part of Dauphin County. Gina Murphy did not return a message left on her cellphone Thursday.

Murphy told investigators her ex-husband had repeatedly threatened her with knives and would leave threatening notes for her in the home, according to court papers.

During an interview with police, Murphy also said she “used her computer to Facebook her friends telling them of the arguments and threats from Daniel.”

Any history of violence between the couple is going to be key to the outcome of any case if charges are filed, said Carlisle attorney Jay Abom of Abom & Kutulakis.

“If she knows he’s been violent in the past, she’s allowed to consider that when she decides to use deadly force,” Abom said. “His history of violence [against her] is relevant in her estimating the necessary use of force.”

Dauphin County Court had no record of protection-from-abuse orders issued by Gina Murphy against her ex-husband, according to a court official. The county’s district attorney, Edward M. Marsico Jr., said he wasn’t aware of police being called to the home on previous occasions.

A neighbor said Tuesday there’d often be parties at the home during the week. The neighbor, Heather Wenrich, also said she noticed several vehicles parked in an alley behind the home several hours before the shooting, indicating they might have had company.

Attorneys say more investigation is needed to determine if Murphy’s actions are supported by the state’s Castle Doctrine, which was expanded last year to give people the right to use deadly force when they feel threatened outside the home.

Under the previous law, people could use firearms or other deadly force without retreating only if they were attacked in their homes, vehicles or businesses.

“You have to immediately believe you were protecting yourself against death or serious bodily injury,” Abom said.

On the night of the homicide, the Murphys had both been drinking, police said. Gina Murphy was drinking at home and at Uncle Jim’s Tavern, according to court papers.

When she returned home from the bar, the couple began arguing, and Daniel Murphy threatened her with a knife. It was at that time that she shot him, according to court papers.

Police obtained a search warrant to search the Murphy’s home for all firearms, including the .22-caliber revolver, ammunition, casings, gunshot residue, knives, knife-sharpening equipment, notes related to Gina and Daniel Murphy, DNA and other evidence.

Results from that search, which was supposed to be completed by Thursday morning, have not been disclosed.

State police said they are investigating the self-defense angle and have not determined if charges will be filed.

Nevertheless, self-defense cases are among the most difficult to prove in court, Abom said.

“Juries have to infer intent,” he said. “It requires jurors to interpret or decide what people were thinking, and that’s not an easy task.”