Authorities also believe at least one of the two Mayes women knew about the bodies, Edwards said. He didn't say which one.
Bain's other two daughters, Alexandria, 12, and Kyliyah, 8 - taken along with their mother and older sister from their home - were believed to still be with Mayes, the FBI said on Monday night.
The Tennessee Bureau of Investigation said it is believed Mayes has changed his appearance and that he may have altered the appearances of his victims, perhaps by cutting and dying their hair.
Bain's husband reported the four missing from their rural western Tennessee home April 27. Mayes, described as a friend of the family who was at their home to help them move to Arizona, was quickly identified as a suspect.
Mayes was last seen in Guntown, north of Tupelo, last Tuesday, according to the FBI.
(Editing by Daniel Trotta and Cynthia Osterman)