A Dutch old master painting stolen by the Stasi, the former East German secret police, has been valued at as much as $2 million for a New York sale on April 15. "Hercules and Achelous" by Cornelis Van Haarlem (1562- 1638) was confiscated from a collector in Berlin after he unknowingly befriended a Stasi informant in 1984, auction house Christie's International said in a statement. The collector recovered the painting last year, following 17 years of legal proceedings that started after the fall of the Berlin Wall. The painting depicts Hercules fighting the river god Achelous, who is in the form of a bull. Stories of loss and recovery can add commercial value to artworks. "The picture's return to its rightful owner is an intriguing story -- and one that is set to add further interest in a magnificent picture," Ben Hall, the head of Christie's old master paintings department, said in an e-mail.