(CNN) -- Steven Spielberg led the FBI straight to a stolen $700,000 Norman Rockwell painting someone snatched from a Missouri gallery. It was in his collection in California.



The original of this Norman Rockwell reproduction was found in the collection of Steven Spielberg last year.



Spielberg wasn't the thief, and he doesn't know who took Rockwell's "Russian Schoolroom" -- an oil of 16 pupils looking at a bust of Lenin. All the A-list director knows is he paid about $200,000 for the 16 x 37 canvas in a legitimate purchase.



The FBI says its just one example of how pilfered art lands in  respectable places. And it was an uncommon ending for stolen art -- someone found it. Recovering masterpieces happens in less than 5 percent of cases, said Bonnie Magness-Gardiner, the FBI's Art Theft Program manager.



Usually, expensive pieces go missing. No one knows who took them. No one gets prosecuted, and everyone wonders, "Why steal something you can't turn to cash quickly?"



Art thieves do a simple risk versus reward evaluation, said Corine Wegener, associate curator of the Minneapolis Institute of Arts.



Thieves know that "even if they receive only a fraction of the work's market value, the cash gained was at low risk of death or injury -- museums can be a relatively soft target," said Wegener, who's teaching a University of Minnesota class this month on art theft.



But it could be years -- or never -- before the thief sees even a small payoff. In 1990, robbers took $300 million worth of certified masterpieces -- among them Rembrandt's "Storm on the Sea of Galilee" and Vermeer's "The Concert" -- from the Isabella Stewart Gardner Museum in Boston, Massachusetts. No one's seen them since.



On Sunday, robbers made off with one of the biggest art hauls in European history, grabbing four paintings worth an estimated $163 million from the E.G. Buehrle Collection in Zurich, Switzerland. They took works by Paul Cezanne, Edgar Degas, Claude Monet and Vincent van Gogh.  See what robbers grabbed in Switzerland »



"These paintings are extremely valuable on the open market, but they'll never go onto the open market. So at the same time they're both priceless and worthless," said Charles Hill, the former chief of Scotland Yard's art and antiques unit.



"Some thieves may buy into the myth that a wealthy but unscrupulous collector will contact them and offer to take the art off their hands," Wegener said. "When this doesn't happen, the thieves often try to ransom the art back to the museum or the insurance company."



One London art dealer, who said he has handled stolen works, told CNN on condition of anonymity that an insurance company would rather get art back at a fraction of its original price than pay the owner its insured value.  Watch how art thieves operate »



Ransoming art to an insurance company through an intermediary adds "up to 10 percent of the market value, which ... given the art market, is quite a lot of money," the dealer said.



David Vuillaume, secretary general of the Swiss Museums Association, told Time magazine that ransom may be what the thieves behind the Swiss heist want.



"We are thinking that maybe in a week or two there will be a ransom demand. But we just have to wait and see," Time quoted him as saying. The museum has offered $90,000 reward for information leading to their recovery, Time reported.



Options for art thieves



Julian Radcliffe, chairman of the Art Loss Register, which operates a database to help recover lost and stolen art, said ransom or reward are unlikely to bring results.



"It is very seldom that people have been able to undertake a ransom," he said. "This gang might think that a reward has been offered, and that they'll get the reward."



But in fact, "the reward won't be paid unless someone is arrested, or there is proper criminal intelligence," and
What was found in Steven Spielberg's collection? Is stolen art easy to find? What are soft targets according to experts? What did experts say about museums?
$700,000 Norman Rockwell painting less than 5 percent museums can be a relatively soft target,"
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