He went on to say that Max had been given an antipsychotic medication that is prescribed for “very advanced forms of schizophrenia in adults.”

“We hope that if the investigation finds that his American parents are guilty of his killing — his assassination — we hope that, of course, they will be brought to justice,” he said.

The authorities in Texas were more cautious in their remarks, saying they were awaiting the results of an investigation. Patrick Crimmins of the Texas Department of Family and Protective Services said his agency had not received any previous accusations of abuse against the Shatto family, and declined to offer any details about signs of physical neglect or abuse.

“We may want to wait for a medical examiner’s report and/or toxicology results,” he said in a statement. In the meantime, he said, Max’s younger brother remains in the Shatto home. “We are monitoring the household to ensure his safety,” he said.

Whatever led to the boy’s death, it was an appalling end to an adoption. A triumphant note on Laura Shatto’s Facebook page last November celebrated her return to Texas with Max and his younger brother, Kirill, 2, whom the Shattos call Kristopher. Natalia Vishnevskaya, the head doctor at the orphanage in Pskov where they were adopted, told Russia’s Channel One that the boys’ biological mother took no interest in the boys’ lives and that her parental rights had been stripped when her sons were 1 and 2 years old.

She said the Shattos had visited the brothers repeatedly at the facility and never aroused any suspicions among the staff.

The Shattos have not given a public account of the boy’s death. A funeral home notice said he “passed into God’s arms on Monday afternoon, Jan. 21.” The obituary read, in part, “Max, you were not with us long enough to leave fingerprints on the walls, but you left fingerprints on our hearts.”