. >> reporter: christopher marinello is an art investigator.s waiting to see if any of the stolen art comes up for sale. after all, if the thieves are after money, they'll try and sell the art so he watches and with a its. >> we'd probably be the first ones to know about it. we do explore a lot of leads. we pass on those leads to law enforcement and let them run with it. >> reporter: investigator robert whitman says whether it comes to stealing art, the actual theft is the easy part. once they have the goods, they need to know how to sell it, without getting caught. >> that's the next step. they're thinking they can sell it just like a car. well, it is not like that. the market for these artworks is very small. >> reporter: according to whitman, nearly all stolen high-end artwork is eventually recovered. investigators continued with their search chasing down countless tips and leads. then, in 1994, a possible breakthrough. that year the museum director received a mysterious unsigned letter post-stamped from new york. the anonymous writer said h