‘Priceless’ Matisse Works Stolen in Daylight Heist of Brazilian Library

Thieves armed with handguns made off with prints from the French painter’s colorful “Jazz” series.

SÃO PAULO—The two men might not have had the brazen ingenuity of the men who broke into the Louvre, but all they each needed was a handgun stuffed down their pants.

São Paulo’s Mário de Andrade library, the scene of the crime.

In the latest daylight robbery to hit the art world, two armed thieves stormed into São Paulo’s marble-floored Mário de Andrade public library Sunday and carried off eight rare prints by the French modernist master Henri Matisse.

The pair lifted their shirts to show the security guard they had guns and threatened an elderly couple, then swiped the artwork off the wall, plopping the pieces into a canvas bag and making their escape in a matter of minutes, witnesses told local media.

Snatching another five works by Brazilian painter Cândido Portinari, the pair escaped on foot from the 100-year-old library, authorities said, one of the city’s most important cultural landmarks. Security footage shows one of the men staggering down the cobblestone sidewalks of São Paulo’s historic center under the weight of the framed prints as people strolled by seemingly unaware of the heist underway.

“Their value is cultural, historical and artistic…economically, they are priceless,” São Paulo’s City Hall said of the works, which included prints from Matisse’s colorful 1947 “Jazz” series. Sotheby’s has described them as among the artist’s most seminal works.

São Paulo’s mayor Ricardo Nunes said Monday police had arrested one suspect—identified by local media as a 31-year-old man with convictions for drug trafficking—but were still on the hunt for his accomplice, as well as the artworks.

Sunday’s raid has heightened fears over the safety of the art world’s most priceless treasures, coming less than two months after thieves disguised as construction workers used a mechanical lift to scale the side of the Louvre Museum in Paris and steal the French Crown Jewels.

Even in crime-hardened São Paulo, art heists are rare. Curators warn Sunday’s robbery highlights how public museums and libraries—hampered by tight budgets and aging infrastructure—have become soft targets.

The same library was robbed in 2006, when thieves made off with rare 19th-century engravings by the Swiss artist Johann Jacob Steinmann. Police recovered one of the works 18 years later, seizing it from a Brazilian collector who had bought it from a London auction house.

The struggle to protect cultural heritage arguably is even greater in Brazil, where there is widespread public indifference to the country’s past—in part, a reaction to years of exploitative and violent colonial rule by the Portuguese. When the country’s National Museum in Rio de Janeiro went up in flames in 2018, it was the first time many Brazilians had even heard of it.

Sure enough, the Mário de Andrade Library was conveniently deserted when the art thieves slipped in through the main entrance just after 10 a.m. on Sunday.

It was the final day of the two-month exhibition “From the Book to the Museum,” a collaboration with the São Paulo Museum of Modern Art that displayed rare midcentury books, documents and prints.

Write to Samantha Pearson at samantha.pearson@wsj.com