They're worth half a billion dollars,

and they disappeared 30 years ago.

Whoever finds them will receive

a $10 million reward.

But let's go back to the beginning.

Isabella Stewart Gardner Museum was an art thief's delight.

Millions of dollars worth of artwork.

Rembrandt, Degas, Vermeer.

St. Paddy's Day, 1990.

Two men dressed as police officers show up at the door.

And they say, very dramatically, "Gentlemen, this is a robbery."

There's no shortage of possible suspects.

Boston was the Wild West.

The two front-runners were the Italian Mob or the Irish Mob.

How you doing?

The Mafia knew

that having a stolen masterpiece is a get-out-of-jail-free card.

The Feds will deal with you. They'll let you out of jail.

It was an easy score, as they say on the street.

There were 13 works taken.

Most important, The Storm on the Sea of Galilee.

It's the only Rembrandt seascape in existence.

This was huge, not just locally, but internationally.

In Dublin, stolen art was used by the IRA as international currency.

In Boston, Whitey Bulger provided the IRA with weapons.

-They could be in the Middle East. -Japan.

South America.

What? It's mind-blowing.

I've spent 25 years on this case.

There has to be a way to figure out where these paintings went.

You could potentially get immunity and get $10 million.

That's why it's so confounding.

There's a lot of deaths.

Everybody who apparently did the robbery is whacked.

Artworks connect to the community.

Standing in front of that painting

would be an unbelievable experience.

When I see those frames,

I feel that they are waiting for the work to come back.

They're out there. Somebody stashed them.

Sometimes, it's the next generation.

"Grandpa's dead. Look what we got!"