In the continuing investigation, Tennessee Bureau of Investigation agents on Thursday searched a storage unit that authorities said smelled of decaying bodies.
The head found over the weekend has been tentatively identified as that of 17-year-old Adam Ray Chrismer of Walker County, Ga., and the hands as those of his wife, Samantha Foster Leming, 16.
Authorities said they might have a final identity Thursday.
The missing teens were seen with Howard Hawk Willis, of Chickamauga, Ga., in Johnson City and Walker County. He is in federal custody in Johnson City on charges stemming from an unrelated drug case.
Authorities say Willis is a suspect in the disappearance of two other people as well.
Willis' mother, Emma Elizabeth Hawk, 70, of Johnson City, was arrested Wednesday night and charged with accessory after the fact to first-degree murder and attempt to tamper with evidence, Washington County sheriff's department chief operating officer Leighta Laitinen said.
Willis' aunt, Marie Hawk Holmes, 74, was charged with attempt to tamper with evidence.
Police in Georgia have said Chrismer and Leming were married in August and left willingly with Willis on Oct. 4 from Rossville, Ga., just over the Tennessee border from Chattanooga.
Chrismer's mother filed a missing persons report on her son Oct. 11, saying she had spoken with him by phone on Oct. 6. He told her he was in Johnson City and wanted to return home, according to a police report.
Willis has been in custody since last week, when he arrested in Johnson City at the residence of his aunt and uncle. A $200,000 bond was revoked for Willis, who was awaiting sentencing on federal drug charges, after New York prosecutors learned he was using credit cards belonging to his 70-year-old stepfather, Samuel Johnson Thomas of Cleveland, Tenn.
Thomas has been missing since Oct. 5 and blood was discovered at his residence in Bradley County.
Members of the Bradley County sheriff's department were in Johnson City investigating whether there is a connection between the disappearances of the young couple and Thomas, Capt. Chip Bryant said.
Willis is also at the center of the investigation into the disappearance of his wife, Deborah Willis, from Catoosa County, Ga., more than a decade ago, Bryant said.
``The revelation of these new cases strengthens our theory that he killed (Deborah Willis) many years ago and concealed the body,'' Bryant said.
Court records in New York indicate Willis had been talking to two people about acquiring false identification so he could leave the United States. He was facing sentencing after pleading guilty earlier this year to transporting 2,600 pounds of cocaine to a warehouse in Brooklyn, N.Y.