Police in Virginia are investigating a “claim of self-defense” in what they described as a domestic-related incident that left one man fatally shot and his girlfriend injured over the weekend.

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The Washington Post reports that Fairfax County police spokesman Sgt. Ian Yost says the woman’s 19-year-old son is believed to be the shooter and he was taken into custody as detectives investigated the circumstances of Saturday's shooting inside a Hybla Valley-area home.

Yost says the teen is cooperating. Public Affairs Director Anthony Guglielmi says police are formally investigating a “claim of self-defense,” but that isn't the final charging decision. It's not clear how the teen's mother was hurt, but she's expected to survive.