Local authorities say it's not clear if she broke any laws.
The 7-year-old boy, Artyom Savelyev, who was called Justin Hansen by the Tennessee family, was put on a plane with a note saying his adoptive mother no longer wanted to parent him because he was violent and had severe psychological problems.
While her actions were condemned by Russia's president and U.S. diplomats, the sheriff investigating the case said it's not clear if anyone can be charged.
"You know, you look at it and it's hard to say exactly if a law has been broken here," Bedford County Sheriff Randall Boyce said. "This is extremely unusual. I don't think anyone has seen something like this before."
That, says Tom DiFilipo, President of the Joint Council on International Children's Services, would be a "real shame."
"We join in the collective outrage over this situation and the decision of the part to send Artyom back to Russia," he said on "The Early Show Saturday Edition." "We also think it would be a real shame and not a service to children at all if international adoption was to be suspended over the misguided action of the parents in Tennessee. Certainly, there's ... literally tens of thousands of successful (international) adoptions."
The parents, he told CBS News Correspondent Rebecca Jarvis, had "many, many many options The last thing you want do is call a travel agent and send a child back to their country of birth. They could have called their local church. There's plenty of parent support groups, some of which are focused exclusively on children from Eastern Europe, including Russia. There's psychologists, school counselors, social services by the state. They could have called their adoption agency, which has licensed staff to assist in these types of situations. Many, many options."
CBS News Travel Editor Peter Greenberg told Jarvis another issue in play is the " chain-of-custody situation. Who had custody of the kid, who provided documentation that was properly notarized and accepted, and then was he traveling on a U.S. passport, a Russian passport, and at what point does the airline accept liability?"
United Airlines, Jarvis pointed out, denies wrongdoing.
"There are too many unanswered questions," Greenberg says. "But the real key is the child custody situation in this country, with so many children of divorce traveling between parents. So there's case history here, where one parent has to provide a notarized document of approval allowing the other parent to take the kid out of the country. In this situation, nobody was taking the kid, the kid was just put on the plane. And once the airline accepts that child, that's where the responsibility starts."
The boy's adoptive grandmother, Nancy Hansen of Shelbyville, said he was violent and angry with her daughter. She said she flew with the boy to Washington and then put him on a plane to Moscow.
"He drew a picture of our house burning down, and he'll tell anybody that he's going to burn our house down with us in it," she told The Associated Press in a telephone interview. "It got to be where you feared for your safety. It was terrible."
Authorities in Tennessee were investigating the adoptive mother, Torry Hansen, 33.
Bob Tuke, a Nashville attorney and member of the American Academy of Adoption Attorneys, said abandonment charges against the family could depend on whether the boy was a U.S. citizen.
It wasn't clear if the adoption had become final. A Tennessee health department spokeswoman said there was no birth certificate issued for the boy, a step that would indicate he had become a U.S. citizen.
The sheriff said Hansen initially agreed to be interviewed by authorities but then postponed it after talking to a lawyer.
Boyce said it would be difficult to substantiate claims by Russian officials that the mother mistreated the child.
"We're here, and the child is in Russia, so it's hard for us to know whether this child has been abused," Boyce said.
The boy arrived unaccompanied in Moscow on the United Airlines flight on Thursday. It had come from Washington. The Kremlin children's rights office said the adoptive mother wrote in her note she was returning him because of severe psychological problems.
"This child is mentally unstable. He is violent and has severe psychopathic issues," the letter said. "I was lied to and misled by the Russian Orphanage workers and director regarding his mental stability and other issues. ...
"After giving my best to this child, I am sorry to say that for the safety of my family, friends, and myself, I no longer wish to parent this child."
Russian Foreign Minister Sergey Lavrov called the family's actions "the last straw" in a string of U.S. adoptions gone wrong, including three in which Russian children had died in the U.S. The cases have prompted outrage in Russia, where foreign adoption failures are reported prominently.
Russian President Dmitry Medvedev strongly condemned the family's actions.
A freeze on adoptions could affect hundreds of American families. Last year, nearly 1,600 Russian children were adopted in the United States, and more than 60,000 Russian orphans have been successfully adopted there, according to the National Council For Adoption, a U.S. adoption advocacy nonprofit group.
The boy was adopted in September from the town of Partizansk in Russia's Far East.
Nancy Hansen, the grandmother, rejected assertions of child abandonment. She said he was watched by a United Airlines flight attendant and that the family paid a man $200 to pick the boy up at the Moscow airport and take him to the Russian Education and Science Ministry.
Nancy Hansen said a social worker checked on the boy in January and reported to Russian authorities that there were no problems. But after that, the grandmother said incidents of hitting, kicking and spitting began to escalate, along with threats.
She said she and her daughter went to Russia together to adopt the boy, and she believes information about his behavioral problems was withheld from her daughter.
"The Russian orphanage officials completely lied to her because they wanted to get rid of him," Nancy Hansen said.
She said the boy was very skinny when they picked him up, and he told them he had been beaten with a broom handle at the orphanage.
There was no response to a knock at Torry Hansen's door, and a phone listing couldn't be found for her. Her mother also declined to put AP in touch with her.
The U.S. ambassador to Russia, John Beyrle, said he was "deeply shocked by the news" and "very angry that any family would act so callously toward a child that they had legally adopted."
Anna Orlova, a spokeswoman for Kremlin's Children Rights Commissioner, said she visited the boy and he told her that his mother was "bad," "did not love him" and used to pull his hair.