Police say Brittany Norwood, 28, is now the prime suspect in the murder of 30-year-old Jayna Murray.
The killing happened at the upscale Lululemon Athletica store near Washington, D.C. March 11.
According to police, Norwood originally claimed both she and Murray were sexually attacked and beaten by two masked men during a robbery attempt.
However, investigators said forensic evidence did not support Norwood's story.
Officials said that tests indicated Norwood was not sexually assaulted and that Norwood appeared to have self-inflicted, superficial scratches.
According to court documents, police believe Norwood killed Murray at the store after it closed for the night, then hurt herself and posed with her hands tied above her head so police would think they were both attacked.
Workers at a nearby Apple store told police they heard two women arguing the night Murray was killed.
The Lululemon shop remained locked Monday morning, with strips of yellow police tape still attached to the door and its windows covered from view by large pieces of brown paper. Businesses along the street displayed white ribbons in Murray's memory.
The killing stunned residents and workers in Bethesda, where violent crime is rare.
The Associated Press contributed to this report.