US marshals delivering an eviction notice found the decomposing bodies of four young people and took into custody a woman who had answered the door.
Investigators were trying to determine whether the woman was related to the dead, who had been dead at least two weeks, authorities said. Her name was not released.
"She was apparently calm throughout," US Marshals Service spokesman Cole Barnhart said.
Mayor Adrian Fenty said the condition of the bodies made it difficult to identify them. "It is going to take scientific tests run by the chief medical examiner's office," he said.
Police Chief Cathy Lanier said the bodies appeared to be of females ranging in age from 5 to 18. Authorities were investigating how and when they had died.