FAIRFAX COUNTY, Va. (DC News Now) — A man died after a stabbing at an apartment in the Mount Vernon area of Fairfax County Sunday night.

The Fairfax County Police Department said emergency dispatchers received a call from a teenage boy who said he stabbed his mother’s boyfriend who was assaulting her.

When officers got to the apartment in the 7900 block of Janna Lee Ave. shortly before 10 p.m., they found all three there. Medics took the man who’d been stabbed, Marcus Roberson, 32, of Washington, D.C. to the hospital where he died.

Police took the teenage boy into custody.

The Fairfax County Police Department said later in the day Monday that detectives determined Roberson was visiting the apartment when a verbal fight escalated into a physical assault. They boy said he stabbed Roberson to stop it.

Police said three other children were in the apartment and that they were not hurt. Medics treated the mother at the apartment for injuries that weren’t life-threatening. Detectives released the boy into his mother’s custody. As of late Monday, he did not face charges.

Detectives still were looking into the circumstances that led up to the stabbing, investigating it as a possible homicide. They planned to consult with the Office of the Fairfax Commonwealth’s Attorney to determine if charges will be filed at a later date.