From nola.com:

David Duke, a former Louisiana legislator and Grand Wizard of the Knights of the Ku Klux Klan, has been arrested in Germany, he confirmed on his web site Tuesday. He said he has since been released from jail.
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The Huffington Post reports that his arrest appears to be tied to Duke’s expulsion from the Czech Republic in 2009. He was detained there on suspicion of denying the Holocaust, a crime in many European countries, including Germany. The Cologne police statement said that Duke “was not entitled to stay in Germany” because of a travel ban against him in another, unspecified European country.

Duke spent a year in an American prison in 2003 and 2004 after pleading guilty to tax fraud and stealing money in supporters donations to pay gambling debts.