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Authorities on Friday freed a Russian billionaire following four days of questioning in connection with an investigation into a suspected prostitution ring at the swank Alpine ski resort of Courchevel, a prosecutor said.

Mikhail Prokhorov, who made his fortune in nickel and gold mining, was among 26 people taken in for custody Tuesday following a six-month investigation.

Although Prokhorov and four others were released, they have all been designated material witnesses in the investigation, said prosecutor Xavier Richaud. That means that no charges were filed, but does not exclude the risk — however slight — that charges could be filed if the investigation shows there is cause.

"There was a lot of agitation, a lot of noise for nothing. These were evenings and trips arranged by tour operators," said lawyer Yvan Guillotte, whose client was described as a Russian manager of Prokhorov's firm, Norilsk Nickel.

Large black cars with tinted windows were seen leaving the Justice Palace in Lyon, apparently whisking off the five. Richaud said the investigation was continuing but indicated they were free to return home because no judicial controls were placed on them.

Asked if they were returning to Russia, or to Courchevel, he replied, "That is not our problem."

The 6-foot-7 Prokhorov is often described as Russia's most eligible bachelor. Even among Russia's big-spending business elite, he has a reputation for organizing lavish parties.

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He is ranked No. 89 on Forbes magazine's 2006 list of the world's richest people. He is worth $6.4 billion, according to Forbes, largely thanks to his holding in OAO Norilsk Nickel, the world's largest nickel producer, and Polyus Gold, Russia's biggest gold miner.

Prokhorov, 41, has used his wealth to acquire Euroleague basketball champions CSKA. He divides his time between Norilsk, Moscow, Saint Tropez on the French Riviera, and Courchevel, where he owns a chalet.

Investigators suspect Russian call girls were brought to the resort, in the Lyon region of France, and paid mainly with gifts from luxury boutiques — a tactic that could complicate efforts to prove the women were prostitutes and not simply friends.

A total of 26 people were taken in for questioning Tuesday, Richaud said.

Richaud said that three judges specialized in organized bands were continuing the investigation, but provided no details.

An Austrian who runs a travel agency, initially suspected of helping Russian girls make their way to two luxury hotels at the ski resort, was among the five freed. Richaud and a police official identified him as Paul Kirchmair, of a travel agency called VCI.

The arrests occurred in several hotels at fashionable Courchevel, which has its own airstrip that can accommodate private jets. Russian tycoons flock to the resort over the New Year and Orthodox Christmas holidays.

Investigators also seized $65,000 at two four-star hotels in Courchevel, an official working on the probe said. The official was not authorized to speak to the media and requested anonymity. No drugs or weapons were found.

Based on Russia's Arctic edge in the Taimyr Peninsula, Norilsk Nickel also has the world's biggest reserves of palladium, and its mines were at one point worked by inmates of Josef Stalin's gulag.