Prominent Russia critic and financier Bill Browder was temporarily detained by Spanish police on Wednesday over a Russian arrest warrant. There was conflicting information over whether the tax evasion warrant was valid.

"Just was arrested by Spanish police in Madrid on a Russian Interpol arrest warrant. Going to the police station right now," Browder wrote in his Twitter account of the incident, delivered almost in real time.

The US-born British hedge fund manager has a tense history with the administration of Russian President Vladimir Putin. At one point his firm, Hermitage Capital Management, was the largest foreign portfolio investor in Russia. However, beginning in 2005, Browder was barred from entering Russia – according to Moscow, because he was a threat to national security, but according to Browder, because he exposed corruption.

Things took a turn for the worse in 2009, when Browder's employee Sergei Magnitsky died in prison after accusing a number of Russian officials of involvement in a tax fraud scheme.

In 2012 Browder successfully lobbied the US Congress to pass the Magnitsky Act, which officially held the Kremlin responsible for Magnitsky's death. In retaliation, Moscow barred US adoptions of Russian children.

Since then, Russian courts have convicted Browder of tax evasion in absentia multiple times.

Browder in Madrid to present Magnitsky evidence

Browder said he was in Spain "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."

Spain is one of 15 countries allegedly used to launder 30 million euros ($35 million) connected to Magnitsky's death. Browder later said he was able to meet with Grinda after his release from Spanish custody.

Spanish authorities said that he was arrested in error and released when they found the Interpol warrant against him to be outdated and therefore invalid, details Browder disputed: "Just to be clear, my arrest this morning in Madrid was the result of a SIXTH Russian arrest warrant using Interpol channels. It was NOT an expired warrant, but a live one. Interpol is incapable of stopping Russian abuse of their systems.

Global criminal justice watchdog Fair Trials also criticized Russia's abuse of the Interpol warrant system, but said that "Interpol should scrutinize alerts before it puts them out through its international networks… Spain should also exercise sense and discretion before arresting people. The result could have been very different if it weren't for Browder's high profile."

es/msh (AP, Reuters)