A detained billionaire who made a fortune as a middleman in Russia’s murky gas trade with Ukraine may hold the key for U.S. lawmakers seeking harsher sanctions against President Vladimir Putin’s inner circle.

Ukrainian Dmitry Firtash, arrested in Vienna this month on an American warrant for bribery and other charges, may hand over a treasure trove of information about deals involving Russian state gas exporter OAO Gazprom that the U.S. would consider corrupt, said Mikhail Korchemkin, a former analyst for the Soviet Union’s Gas Ministry in Moscow and founder of Malvern, Pennsylvania-based East European Gas Analysis.

After Putin seized Ukraine’s southern Crimea region, a U.S. Senate panel approved a bill on emergency funding for the country that would widen the scope of sanctions to include any Russian involved in “significant” corruption.

“This law would enable the U.S. to go after any member of Putin’s entourage,” Masha Lipman, an analyst at the Carnegie Moscow Center, said by phone. “The point is to deepen the fractures within the Russian elite. The idea is to weaken Putin so he can be contained.”

President Barack Obama last week expanded financial sanctions to 20 more Russian officials, billionaires and a bank, including brothers Arkady and Boris Rotenberg, who have joint investments with Firtash in Ukraine and Russia. The Rotenbergs’ companies received $7 billion of contracts for the Sochi Winter Olympics and are major suppliers to Gazprom.

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Firtash, 48, built his fortune as a broker of Russia’s gas sales to Ukraine, one of Gazprom’s biggest export markets. He and a partner owned half of RosUkrEnergo, which was founded in 2004 and emerged as Ukraine’s sole gas importer in 2006 to 2009, between price disputes with Russia that led to supply halts and shortages across Europe.

Gazprom oversaw the other half of RosUkrEnergo, which Ukraine’s security service in 2005 said may be indirectly controlled by Semion Mogilevich, an organized crime suspect on the U.S. Federal Bureau of Investigation’s most-wanted list. Firtash has repeatedly denied any link between Mogilevich and RosUkrEnergo. A lawyer for Mogilevich, who lives in Moscow, said his client has never been in business with Firtash.

Still, the former U.S. ambassador in Kiev, William Taylor, said Firtash himself told him that he needed Mogilevich’s permission to get into the lucrative gas business with Gazprom, according to a secret cable to the Central Intelligence Agency that was published by Wikileaks and dated Dec. 10, 2008.

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