FAIRFAX COUNTY, Va. (WRIC) — A teenager is in custody in Fairfax after police say he fatally stabbed his mother’s boyfriend, who he said was assaulting her.

According to the Fairfax County Police Department, officers were called to an apartment on the 7900 block of Janna Lee Avenue in the Mount Vernon area just before 10 p.m. on Sunday, Jan. 29 after a teen reported that his mother was being assaulted by her boyfriend.

Before officers arrived, police said the teen stabbed the boyfriend, who was taken to a local hospital and pronounced dead. The teen is in custody and police are working to determine what led to the stabbing and whether what he initially reported is accurate.

Anyone with information related to this incident is asked to call Fairfax Police at 703-691-2131.