"They did know of each other, but (to what extent) is not known," TBI spokeswoman Kristin Helm said Wednesday.
Tenth District Attorney General Steve Bebb said he was told "they had some mutual acquaintances, and that is how they met."
Miller, 60, was a lifelong Sweetwater farmer who knew many people through his political activities and excavating business. His alleged killer's last known address was in Sweetwater.
Records show she has used several names in the past and has a criminal record for minor drug offenses. The indictment in the Miller case identifies her as simply Jessica Kennedy.
She is charged with four offenses: felony murder, aggravated robbery, arson and abuse of a corpse. A grand jury indicted her Wednesday, based on findings of a multi-agency investigation led by TBI.
Because of Miller's size and strength, nearly all of his friends strongly felt he could not have been subdued, or his body moved, by just one person. Records list Powers as 5 feet, 7 inches tall and weighing 132 pounds.
Asked if there are any other suspects or if any other arrests were expected, Helm's answer was: "At this time, no other case has been presented to the grand jury."
"I don't know of any other suspects, but I know the case is still under investigation," Bebb said.
According to the indictment, Powers killed Miller "during the perpetration of robbery."
Wording of the indictment also indicates that she used a handgun to rob him of money before killing him, rather than killing him first and then robbing the corpse.
It was widely known that Miller commonly carried large sums of cash.
Helm declined to say if a weapon has been recovered.
Officers arrested Powers in the Meigs County Jail, where she was serving time for a probation violation from a charge of simple possession of narcotics. She was transferred to the Monroe County Jail, where she is being held under $500,000. Arraignment is scheduled for Jan. 18.
Miller was last seen alive leaving the election commission office shortly after noon July 17. His body was found later that afternoon on Sands Road in the trunk of his flame-engulfed car. He had been shot in the head three times, and his body was burned beyond visual recognition.