A man in his 40s has been arrested on suspicion of murdering the 34-year-old former marine, who moved to the country in 2019.
The body of an American student who went missing last week has been found in a wooded area in Russia.
Catherine Serou, 34, was a former marine and law student at Lobachevsky University in the western Russian city of Nizhny Novgorod.
She vanished on Tuesday evening, prompting a volunteer-led search operation involving 100 people to get under way on Thursday.
Serou's body was found in the forest north of the Bor district on Saturday, according to Russian media.
Russia’s Investigative Committee, which probes major crimes, later confirmed it had found the "missing foreign student".
An unarmed 44-year-old man was arrested on suspicion of murder. If convicted on this count, he would face up to 15 years in prison.
Serou's mother Beccy Serou told NPR on Friday the last message she received from her daughter had read: “In a car with a stranger. I hope I'm not being abducted.”
Her daughter, she said, had wanted to study Russian before applying for law school in the United States and pursuing a career as an immigration lawyer.
The U.S. Embassy in Moscow has said it is "closely monitoring" the local authorities' investigation and providing "all appropriate assistance" to Serou's family.