Yevgeniy Nikulin, 29, faces extradition requests from both countries after being detained by Czech police on an Interpol arrest warrant issued by US authorities.
Nikulin, a Russian citizen, was arrested in a restaurant in Prague on 5 October shortly after arriving in the city during a holiday with his girlfriend.
A federal court in Oakland, California, followed up with an indictment charging him with offences relating to the hacking of computer networks belonging to LinkedIn, Dropbox and Formspring and formally requesting his extradition to the US.
He faces a maximum 30 years in prison and up to US $1m in fines if convicted on charges including computer intrusion, aggravated identity theft, conspiracy, damaging computers and trafficking in illegal access devices.
There is no acknowledged link between Nikulin’s alleged offences and the hacking of Hillary Clinton’s presidential campaign, but his arrest came just three days before the Obama administration formally accused Russia of stealing emails from the Democratic National Committee and disclosing them through WikiLeaks.
Formspring, one of the sites he allegedly hacked, was the platform used for sexting by Anthony Weiner, the former New York mayoral candidate and husband of Huma Abedin, Clinton’s closest aide. The discovery of emails linked to Clinton on Weiner’s laptop damaged her campaign in its final two weeks after FBI director James Comey revealed their existence.
Meanwhile, Russia has responded to the American extradition request against Nikulin by tabling one of its own, demanding that he be returned to face allegations dating back to 2009 that he hacked another person’s bank account and stole 111,000 roubles (£1,465).
“He was never formally accused at that time. I think the reason is that he was recruited [by the Russian security services],” said Ondrej Kundra, political editor with the Czech weekly magazine Respekt, which has reported that the Russian services offer alleged offenders immunity from prosecution in exchange for collaboration.
“There’s intense lobbying in this case. People from the US and Russian side are talking to the Czech authorities because both really want Nikulin in their countries.”
One theory is Nikulin — even if not personally involved in the election hacking — may know other hackers who were.
Fuelling speculation is the existence of sealed US court documents, tabled six days after the original indictment against Nikulin on 20 October but whose contents have not been revealed.
“A number of documents were filed under seal, which means you cannot talk about them,” a US justice department spokesman told the Guardian.
Adam Kopecky, Nikulin’s Czech lawyer, said his client denied both the US and Russian charges and suggested he had become a political pawn. “My client and myself think it’s a political affair,” Kopecky said.
“Given the international situation, when one superpower accuses a citizen of the other of hacking their computers and then the other superpower accuses the same citizen of another crime, it’s kind of strange.”
Nikulin has suffered health problems since his arrest, his lawyer said.
Kopecky lodged an official complaint after prison authorities put his client under high-level supervision that included monitoring his communications with the lawyer.
“He is unhappy about being detained for a long time in a foreign country and about the accusations against him. He wants to return to Russia — but as a free man,” Kopecky said.
Czech television has reported that FBI agents are to travel to Prague to question Nikulin in the presence of Czech authorities. An FBI spokesman refused to confirm that but said the bureau was “aware of the situation”.
The case is currently in the hands of Prague’s chief prosecutor, who is expected to issue a decision on the twin extradition requests at the end of this month or early in February, a spokeswoman for the city’s municipal court said.
Russia’s embassy in Prague declined to comment but cited a previous foreign ministry statement in which a spokeswoman compared the affair to other incidents and called it “another proof that the US law enforcement agencies are hunting for Russian citizens across the world”.
A 32-year-old Russian computer programmer named only as Lisov was arrested by Spanish police at Barcelona airport this month on another US arrest warrant. Police in Spain said he was suspected of leading a financial fraud network and having designed and used software to steal account details from banks and individuals.
Another Russian citizen, Roman Valerevich Seleznev, was convicted last year of 38 hacking-related charges by a US court after he was arrested and extradited from Guam in 2014. Russia said Seleznev’s arrest amounted to “kidnapping”.