Financier Bill Browder was held in Madrid on Wednesday apparently under a Russian arrest warrant over allegations of fraud.
The Russians have repeatedly tried to get Interpol to issue an arrest warrant for Browder.
Browder, who gave up his US citizenship in 1998, was named in a "diffusion notice" by the Russian government in October which allows a country to temporarily bypass Interpol headquarters and notify a country that another country is seeking the arrest of a specific person.
Browder has since led an worldwide campaign to impose additional sanctions against Russian officials and he's been widely credited for the creation of the Magnitsky Act in the United States. "They won't tell me which station", the tweet reads.
The Magnitsky Act returned to the headlines in 2017 after it emerged that a lawyer supporting the Russian government's position had met senior figures in Donald Trump's United States presidential campaign, including Trump's son and son-in-law.
Police found out there that the order was no longer valid, she said.
However, in an email, Interpol said it has never issued a Red Notice for Browder.
Shortly after leaving the police station, Browder tweeted a curbside photo and wrote: "Good news".
Recall, 11 July 2013 the Moscow city court recognized the General Director of investment Fund Hermitage Capital Management William Browder guilty of tax evasion and sentenced him to 9 years in a General regime colony. He tweeted on Wednesday morning that he'd been arrested on an Interpol warrant, but the global law enforcement agency denied involvement.
He has been one of the main proponents of the Russian Federation sanctions law in the USA known as the Magnitsky Act - named for his former lawyer Sergei Magnitsky, who died in suspicious circumstances in 2009.
Browder, the CEO of Hermitage Capital, made billions during Russia's chaotic and devastating "shock therapy" in the 1990s.
"Moscow should concentrate on bringing those responsible for the murder of #Magnitsky to justice", Johnson added.
He said he had travelled to Madrid "to give evidence to senior Spanish anti Russian mafia prosecutor Jose Grinda about the huge amount of money from the Magnitsky case that flowed to Spain".
"The most important thing is that they informed all member states not to entertain any notices against me going forward from Russia", Browder said in an interview.