Investigators have opened a murder case into the death of a 9-year-old Russian boy in the care of a U.S. family, the Investigative Committee said in an online statement late Monday.
Anton Fomin died of smoke inhalation in a fire at his house in Nebraska in May.
Local authorities could not determine what caused the fire and did not find evidence of criminal behavior, The Associated Press reported at the time.
But Russian officials have said that Fomin's death was suspicious. "The child was left alone," and his body was found in the basement, children's ombudsman Pavel Astakhov tweeted Tuesday.
Astakhov earlier said the boy was locked in a cellar, a charge Fomin's guardian denied.
Although the Investigative Committee's statement says that Fomin was adopted in Russia, the U.S. Embassy in Moscow released a statement shortly after the boy's death saying there was no intercountry adoption involved.
Fomin was brought to the United States by his biological parents in 2005 and later placed in the care of an American family that attended the same church as his parents.
U.S. families have adopted an estimated 60,000 Russian children in the past two decades. At least 20 have died, sparking outrage from some Russian officials, led by Astakhov, a close ally of President Vladimir Putin.
Russian investigators have opened 11 mostly symbolic criminal cases in connection with the deaths, claiming that several were not adequately adjudicated by U.S. courts.
One of them appeared to be stymied Tuesday, when a Moscow court refused to order the arrest in absentia of an American accused of killing his adoptive Russian son in 2005, citing the man's acquittal by a U.S. court.
News of the death of 3-year-old Max Shatto, a Russian boy adopted by U.S. parents, last month sparked the latest dispute between the United States and Russia over bilateral adoptions.
Citing the safety of Russian children following a string of abuse scandals going back several years, the government banned U.S. adoptions as of Jan. 1.
The move was widely seen as a response to a U.S. law that called for sanctions against Russian officials suspected of human rights abuses, and critics said officials failed to put the U.S. deaths in context.
Up to 300 orphans entrusted to Russian families die every year, according to State Duma Deputy Yelena Mizulina, head of the Duma's Committee on Family, Women and Children, Gazeta.ru reported.