Barbara Ann Evans, 65, is accused of killing Don Barker, 62, and his wife, Sue, 63, and James Powell, 74, and his wife, Ruth, 71.
The Charlotte Observer reports Evans allegedly frequented the Barkers' convenience store and James Powell was a friend of Evans' late husband.
The Powells were shot and killed at their home in January 2005. The Barkers were shot to death at home the following September. Police have released no clear motive for the killings.
Police said the same gun was used for all four killings, and Detective Sgt. Ron Wyatt said Evans received four handgun permits in 2004. Sheriff Phil Redmond said Wednesday Evans was the only one of 700 people interviewed by police who knew all four victims.
Evans, due in court Aug. 14, was being held without bond Thursday in the Iredell County jail. She has requested a court-appointed attorney.