PORTLAND, Ore. (AP) — A 20-year-old man is facing murder charges in the death of a 22-year-old woman, Gresham police said Monday.

Brian Washington II was arrested Sunday after police began investigating the death of Iryonna Bynum at a Gresham home. Police initially responded to the home Tuesday on reports that a woman, later identified as Bynum, was not breathing.

Police would not say whether Bynum died at the home or at a hospital, and they did not specify the manner in which she was killed, The Oregonian/OregonLive reported. But they said an autopsy revealed the cause of death was homicide.

Washington has pleaded not guilty to one count of second-degree murder constituting domestic violence. While the charge includes a domestic violence component, police have not specified the nature of their relationship.