A woman was found dead underneath a bridge in Northwest Washington early Saturday, and police are working to identify her and determine how she got there, authorities said.

Police were first tipped to the unusual incident just after 6:40 a.m., when a passerby called 911 to report that there was an unconscious woman underneath the bridge on Massachusetts Avenue that runs over Rock Creek Park near the Islamic Center, said Officer Araz Alali, a D.C. police spokesman. Alali said the woman was unconscious, not breathing, and was pronounced dead on the scene.

Alali said police are still working to identify the woman and determine what happened to her. He said police had not ruled the case a homicide, and he declined to say if the woman had suffered any sort of trauma.

“We’re not saying it’s suspicious, but we are vigorously examining this,” Alali said. “It’s an open investigation.”

Alali said the woman was “older,” but declined to give even a general age range.