Prosecutors and state police are trying to determine whether the fatal shooting Saturday of a 19-year-old man was justified.

Montgomery County District Attorney Risa Vetri Ferman would not identify the shooter, who told police he pulled the trigger after the two men attacked him with baseball bats and refused to back down.

"We will identify him only if he is charged," Ferman wrote in an e-mail. Police questioned the man and released him.

The man shot and killed one of two assailants who came after him with baseball bats outside his house. The other man was wounded in the arm.

Ferman issued the following account of the Dec. 17 shooting at 1705 Snyder Rd. in Upper Frederick Township:

Ferman said a woman living with her boyfriend contacted her husband to pick her up after she and the boyfriend argued.

Her husband, Joshua Levin, and son, Zachary Levin, 19, both of Barto, arrived at her boyfriend's home wielding baseball bats, one a full-size aluminum bat, the other a small wooden replica.

Ferman said the man retreated to the rear of the property, where his truck was parked. Joshua and Zachary Levin followed and threatened to kill him.

The resident retrieved a Ruger .40 caliber semiautomatic handgun from under the front seat of his truck, Ferman said. The gun was legally owned and registered to the resident, who has a valid license to carry firearms.

Zachary Levin struck the man with his bat, and the man fired a single shot. Joshua Levin approached with his bat, poised to strike, and the man fired again.

State police found Zachary Levin with a fatal gunshot wound to the chest. Joshua Levin had been shot in the arm.

The Montgomery County Coroner's Office conducted an autopsy and ruled Zachary Levin's death a homicide.

Whether the homicide was justifiable will turn on the reading of a law enacted in August.

Under the Castle Doctrine, a person may use deadly force to protect himself or herself from death or serious injury when an assailant displays a deadly weapon as long as the person is not committing a crime.

The investigation is continuing, and the results of ballistics and toxicology results are pending, Ferman said.

Contact staff writer Bonnie L. Cook at 610-313-8232 or bcook@phillynews.com.