A man was fatally shot inside a Fairfax County home Saturday, and police said they are investigating “a claim of self-defense” in what they described as a domestic-related incident.

A woman was injured in the Hybla Valley-area home, and Sgt. Ian Yost, a Fairfax County police spokesman, said the man killed had been her boyfriend. The woman’s 19-year-old son, who was believed to be the shooter, was taken into custody as detectives investigated the circumstances, Yost said.

“Initially, we called him a suspect. He was changed to a person of interest,” Yost said. “He is cooperating with detectives.”

Anthony Guglielmi, director of public affairs for Fairfax County police, said Sunday that after consultations with the commonwealth’s attorney and “initial interviews and a preliminary review of the crime scene, we are formally investigating a claim of self-defense.”

Guglielmi said that “this is not the final charging decision” and that more interviews are needed, “but at this point, no charges have been filed.”

The shooting occurred in the 7900 block of Janna Lee Avenue. The woman was taken to the hospital and is expected to survive. Police originally described her injury as a gunshot wound but later said it wasn’t clear how she was hurt.