Bill Browder, the hedge fund manager who has become a crusader against Russian corruption, said the arrest of Vladimir Yevtushenkov was intended to send a message to any oligarch plotting moves against Putin, as the value of their assets drops in the wake of western sanctions.
Yevtushenkov was released on Friday, after being put under house arrest for three days on charges of money laundering.
As the richest man to fall into the hands of the Russian justice system since Mikhail Khodorkovsky was arrested in 2003, Yevtushenkov's detention heightened speculation that the Kremlin wanted to take control of his oil company, Bashneft – one of the few Russian energy companies still in private ownership.
Speaking before Yevtushenkov's release, Browder said the arrest was "more motivated by paranoia than any demand for a particular asset", because "Putin and his underlings can always steal these assets in any number of ways".
"I don't know if Yevtushenkov did anything more or less irritating to Putin than the other oligarchs. I just think [Putin] randomly picked one out to make sure none of the other oligarchs are going to start challenging him or start planning any palace coups.
"Now that their wealth has been diminished by Putin's actions, they have a big incentive to act against Putin and he knows that."
Russia's main stock market, Micex, has lost 6% of its value since the west tightened economic sanctions against Russia in July over its threat to the sovereignty of Ukraine, and the value of the rouble has fallen to all-time lows against the dollar.
Browder is seeking to hold to account low-level Russian officials whom he believes are responsible for the death of his lawyer, Sergei Magnitsky, who died in a Moscow jail in 2009 a year after reporting a massive tax fraud to the authorities.
Browder himself was blacklisted by the Russian government in 2006 after 10 years of investing in the country through his Hermitage Capital Management fund.
He says he has traced $200m (£123m) of the $230m missing under the tax fraud scheme and is seeking to get the European Union to follow the United States in banning suspected perpetrators from their territory and freezing their assets.
Browder said he was hopeful that one of the EU's 28 member states would put the issue on the agenda before the end of the year. However, he is critical of western countries for having been slow to respond to the crisis in Ukraine. "We would be in a much less dangerous situation if they had gone for targeted sanctions with broad lists of Putin cronies at the very get-go," he said.
Western sanctions are already weighing on Russia's weak economy. The former finance minister Alexei Kudrin recently warned that the government would struggle to help state companies frozen out of western money markets as the economy slides deeper into stagnation.
Yevtushenkov's arrest heightened alarm among Russian business people already uneasy about sanctions. German Gref, an economic liberal who leads state banking giant Sberbank, described it as a tragedy that would have a negative impact on Russia's business climate, while the leader of the main business union collected signatures to petition for Yevtushenkov's release.
The influence of economic liberals in the country has diminished since the onset of the Ukraine crisis, which has bolstered the position of the Kremlin's hawkish siloviki faction of officials with a background in national security.
"Putin's calculus in Ukraine is not economic but geopolitical, so naturally the influence of the liberals has diminished," said Alexander Kliment at the political risk consultancy Eurasia Group. He has observed a deterioration in the business climate over the past year – an area where Russia has never scored highly on international rankings. And as business slows down, the fight for the spoils is intensifying.
"As the economic pie starts to shrink, everyone is sharpening their knives. Those who are closer to the Kremlin will do better than those who are not, and Yevtushenkov was not as close to the Kremlin as others."
While many observers – including Khodorkovsky himself – have drawn parallels to the Yukos case, in which the oil company owned by Khordorkovsky was forcibly broken up over alleged unpaid taxes, Kliment sees some important differences.
Khodorkovsky was arrested at a time when Russia was trying to rebuild its national resources, when oil prices and incomes were rising. Now oil prices are falling and the economy is practically in recession.
"The Russian elite is starting to cannibalise itself."
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