"I am sorry to say that for the safety of my family, friends, and myself," the letter said, "I no longer wish to parent this child. As he is a Russian national, I am returning him to your guardianship."
CBS News correspondent Richard Roth reports the letter was signed, "Torry Hansen."
At a Siberian orphanage, they remember Hansen as the 33-year-old nurse from Tennessee who played happily with Artyom before adopting him last September. But her letter called the boy violent and mentally unstable.
Shown on Russian TV today, talking to a child care official, Artyom's was asked, "did she hit you?"
"No," says the boy, gesturing to show his hair was pulled.
The Seattle agency that arranged the adoption says it's "saddened", but sheds no light on what happened.
The U.S. State Department says it's "troubled" by the case.
Tennessee authorities went to Torry Hansen's home looking for an explanation. Her lawyer says she'll meet with them next week. In Moscow officials say Artyom now needs good care; he needs to be "rehabilitated."