so does anthony amore, who has worked tirelessly to get the artwork back.k you're close? >> i do. i've been saying that for a couple years now and people are going to start to wonder about me. it's a slow process. we liken it to a needle in a hey stack, but we're trying to make the hay stack smaller. >> reporter: and it is getting smaller. 25 years after the crime, investigators say they finally know who was behind it. but their revelation leads to more questions than answers. most of the products we all buy are transported on container ships. before a truck delivers it to your store, a container ship delivered it to that truck. here in san diego, we're building the first one ever to run on natural gas. ships this big, running this clean, will be much better for the environment. we're proud to be a part of that. vo: in the nation, we know how it feels when you aren't treated like a priority. we'll take care of it. we put members first. join the nation. thank you. ♪ nationwide is on your side now with the you can watch live tv anytime. it's never been easier

. >> reporter: anthony amore is an active investigator on this case. he says back in 1990, no one was allowed in to the museum after hours. not even police officers. but rick, the security guard, says he routinely would buzz in museum employees after hours, even the museum's director. >> i was never verbally told that, to the best of my knowledge. i know -- i'm sure there was a policy written somewhere. i'm sure it was. but it wasn't the culture of the place for the most part. people came in and out of there fairly regularly. i mean at least once a month we let someone in. >> reporter: so it was not unusual for rick to hear that buzzer go off. on this night, rick says he had no doubt it trereally was the boston police at the entrance. >> they were standing there in their hats and coaches and badges. they looked like police. i buzzed them into the museum. and one of them came right over to my desk and one of them kind of stood in the alcove right there, just looking around. didn't seem particularly odd to me. and he came up to me. the one guy. and he as

it is a question that continues to puzzle me museum security director anthony amore. >> there were lots you turn around there is a different interesting fact that you find. >> reporter: one of the biggest questions for him -- why did thieves steal what they did? remember path of the thieves on the second floor when they went from the dutch room to the short gallery, bypassing valuable works of art that were small and portable and worth a lot more than some of the other art they stole. >> the two big rembrandts and the vamir, those three pieces account for 90% of let's call it $500 million, $400 million of the value. >> reporter: another big question -- why did the thieves bother taking the golden finial that sat atop a napoleonic flag. >> they wanted very badly to get that flag. that always seemed to me the clue that's most interesting. >> a fascinating hour, fascinating mystery. it starts right now, and here is the cnn special report "the $500 million question who pull d aufed off the greatest art heist?" >>> inside these walls, priceless works of art. but also a mystery that has laste