A Norman Rockwell painting stolen more three decades ago was found in Steven Spielberg's art collection, but the Oscar-winning filmmaker acquired it legally, the FBI said on Friday.Rockwell's Russian Schoolroom, worth as much as $700 000 today, was stolen from a St Louis gallery in 1973 and purchased by Spielberg from a legitimate dealer in 1989, the FBI said in a statement.The Hollywood mogul only realised the stolen origin last week when the FBI posted a picture and description of the painting on a website. The FBI Art Crime Team confirmed a match on Friday.The 40,5cm-by-94-cm, oil-on-canvas painting shows children in a classroom with a bust of Lenin.Spielberg, director of hit movies like ET and Schindler's List, is "cooperating fully" and will retain possession of the painting while its rightful ownership is determined, the FBI said.