WASHINGTON (CNN) -- How did two pricey Van Goghs become Van Gone?That is one of many questions asked by the FBI Tuesday when the agency unveiled its list of the world's "Top 10 Art Crimes," an effort to enlist the public's help in solving some of the world's most famous art heists.The Van Goghs, "Congregation Leaving the Reformed Church in Nuenen" and "View of the Sea at Scheveningen," which are valued at a collective $30 million, are high on the FBI's list of artworks it wants to retrieve. Both were stolen from the Vincent Van Gogh Museum in Amsterdam, Netherlands, in 2002. Two men were arrested in the theft, but the paintings have not been found.Art theft has become a thriving black-market industry that causes global losses of about $6 billion a year, according to the FBI. However, FBI assistant director Chris Swecker said during a Tuesday press conference that the amount isn't precise because art is difficult to appraise. For example, a piece expected to snare $4 million at auction recently sold for $13 million, he said. (Watch the FBI's new art crime team -- 2:04)Saying art theft "impoverishes us all," Swecker said that the "theft of cultural property is a worldwide problem, and the FBI Art Theft Program and Art Crime Team are part of the solution." Making the crimes more serious is that the FBI has evidence of ties to organized crime and terrorism, he said.The stolen works on the agency's list could form an impressive gallery on their own. Along with the Van Goghs are works by Leonardo da Vinci, Paul Cezanne and Michelangelo Merisi da Caravaggio. The institutions that were robbed dot the globe, from Boston to Baghdad.Perhaps the most recognizable masterpiece on the list is Edvard Munch's "The Scream," which was stolen, along with the painter's "The Madonna," from the museum bearing his name in Oslo, Norway, last year. (Full story)The list includes thefts of works other than paintings, such as the $3 million Davidoff-Morini Stradivarius violin, which was stolen in 1995 from the New York City apartment of Erica Morini, a noted concert violinist.In an apparent effort to tout the successes of its year-old Art Crime Team, the bureau also included on the Top 10 list the theft of three paintings that have already been recovered. Two paintings by Pierre-Auguste Renoir and a self-portrait by Rembrandt van Rijn were stolen from the National Museum in Stockholm, Sweden, in 2000. One of the Renoirs was recovered by the Stockholm County Police the next year. A task force of international police agencies, including the FBI, found the other missing Renoir and the Rembrandt this year. The missing Renoir was found in Los Angeles, California, and the Rembrandt was found in Copenhagen, Denmark, according to an FBI press release.Also included on the list are Cezanne's "View of Auvers-sur-Oise;" Leonardo's "Madonna of the Yarnwinder;" Benvenuto Cellini's "Salt Cellar;" Caravaggio's "Nativity;" between 7,000 and 10,000 looted or stolen Iraqi artifacts; and 12 pieces from the Isabella Stewart Gardner Museum (including three more Rembrandts) worth an estimated $300 million. (Wolf Blitzer on how the museum tried to retrieve its artwork in March)The FBI hopes its Top 10 list will increase the visibility of its Art Crime Team, yielding more leads and tips to recover the art, Swecker said. The bureau also has established a tip line on its Web site, www.fbi.gov.