. >> reporter: special agent jake archer is based in philadelphia he and his partner work to make it their business to find stolen treasures. >> it could be artwork, it could be antique guns. you think we're using in revolutionary war. both special agents took us to a nondescript cinderblock building in the tri-state area. behind the door a collection that belongs to a european collection. >> we don't know what's going to come in today, tomorrow or next week. >> reporter: we can't even show you the paintings because of the current investigation but can tell you six of these paintings were recently found in the philadelphia area. the agents won't even say how much the paintings are worth but we know they were stolen in 1988. >> these pieces are incredibly difficult to track. >> reporter: but with the help of the evidence response team, the art crime unit in philadelphia covers the eastern half the pennsylvania. the team's reach is international, recovering millions of dollars of art over the years. they are just one of a few specialists in the entire fbi. they work together with a 16-