By Paula Ebben

BOSTON (CBS) – It’s the greatest unsolved art heist of all time. And now a Dutch private investigator says he has some leads that could solve the case.

Arthur Brand, a private investigator in Holland, has been called the “Indiana Jones of the art world.”

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Brand told WBZ-TV he is negotiating with people who might be able to return the most valuable collection of art ever stolen – paintings taken in the Isabella Stewart Gardner Museum heist in 1990.

Arthur Brand believes he can solve the Gardner Museum art heist. (CBS)

But time is running out for those who want the reward.

“These are some of the most famous paintings ever produced by mankind, and it’s time to bring them back,” said Brand.

Brand is a well-known European art advisor and part-time sleuth who’s had success getting stolen art back. Most notably he helped locate bronze horses that belonged to Hitler – the most important statues of the Third Reich.

“Everybody thought them to be destroyed for 70 years 75 years and then they popped up,” Brand said.

Brand believes the art is in Ireland.

“Former IRA sources have told me or people that I know that there has been talk about these paintings for years within the IRA,” said Brand.

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He says he’s talking with people based on two good leads – one that a famous Dutch criminal showed fresh photos of the art in the 1990s, trying to sell the pieces. The other theory he must keep under his hat.

“We have another lead we cannot say too much. But it has to do with the paintings and the IRA and the Netherlands,” Brand told WBZ-TV.

Empty frame at Isabella Stewart Gardner Museum (CBS)

Brand stresses this case is no longer about arresting people – just getting the pieces back.

“In this case the FBI has assured that nobody will get arrested and they will get a reward and I know the FBI is telling the truth,” he said.

Though there is a $10 million reward available through the end of the year, Brand says that’s not why he’s pursuing the case.

“The $10 million will not be for me. They can give me one beer. That’s enough. And they can go away with the $10 million and we will celebrate all of us the return of these paintings,” Brand said.

“Somebody out there knows where they are.”

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WBZ-TV reached out to Anthony Amore, the director of security at the Gardner Museum. He said they have been aware of the leads, and feel they have covered them.

Paula Ebben