Michael Craver, 47, and Nanette Craver, 56, adopted both children from a Russian orphanage when they were 18 months old.
The couple received a sentence last month of time served -- about 19 months -- after a jury in York County, Pa., convicted them of involuntary manslaughter, two counts of child endangerment and conspiracy in the death of their 7-year-old son, Nathaniel.
Alexander Bastrykin, chief of the Russian Investigative Committee, said in letters to the country's presidential council head and human-rights ombudsman the couple should lose their right to be the parents of Nathaniel's twin sister, Dasha, RIA Novosti reported.
The couple adopted both children from a Russian orphanage when they were 18 months old.
Dasha, Bastrykin wrote, should be returned to Russia.
Nathaniel died at Hershey Medical Center in August 2009 of subdural hematoma, or bleeding on the brain. The jury acquitted the couple of first- and third-degree murder.
The Cravers have said Nathaniel had suffered from fetal alcohol syndrome and other problems that caused him to injure himself accidentally and deliberately.
The Russian Investigative Committee said the sentence wasn't severe enough and called for more investigation.
A Moscow court has refused to approve the couple's arrest in absentia, but committee spokesman Vladimir Markin said Russia would pursue the case against them.
Since 1991, 17 adopted Russian children have died worldwide as a result of beatings or negligence, Russian statistics show, RIA Novosti said.
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