Some expressed fear Monday that works of art are in increasing danger from violent raids - unless, said Deputy Culture Minister Yngve Slettholm, "we lock them in a mountain bunker."
Armed, masked robbers stole a version of "The Scream" and another of Munch's works, "Madonna," from Oslo's Munch Museum on Sunday as visitors watched in disbelief.
Despite numerous tips, police said Monday they have no suspects and no leads about what's become of the paintings.
The motive behind the robbery also remained a mystery. But art experts speculated the thieves were either looking for a ransom or wished to impress other criminals since it would be nearly impossible to sell such famous pieces of art.
Oslo's Verdens Gang newspaper pointed out that the Munch paintings were stolen on the same date, Aug. 22, as "Mona Lisa" was stolen in Paris in 1911.
Whatever the motive, the director of the Munch Museum, Gunnar Soerensen, appealed to the robbers to "please take care of the paintings, no matter what else you do with them."
It's the second time in a decade that a version of the iconic painting has been stolen. Another version of "The Scream" was stolen from Oslo's National Gallery in February 1994, but recovered three months later.
"The Scream" depicts an anguished figure appearing to be screaming, or listening to a scream, while holding his hands to his head. It was loaded into a waiting car along with another famous Munch work, "Madonna." The getaway car and the picture frames were found by police in Oslo hours after the robbery.
The Munch works were not insured against theft, because it was impossible to set a price on them, said John Oeyaas, managing director of Oslo Forsikring, the city-owned company that insure the paintings against damage.
But he said the theft in broad daylight from one of Norway's most visited museums raises the question of security - "How can we make these artworks available to the public while still securing them?"
It's a dilemma shared by museums throughout the world.
The lightly guarded Munch Museum has silent alarms and security staff. But in a country where many police officers do not carry weapons, there was little that unarmed museum guards could do to stop robbers with guns.
"It is food for thought that the spiral of violence has now reached the art world," Slettholm told The Associated Press. "This is a first for Norway."
However, officials said there were no immediate plans to improve museum security.
"We cannot lock up our pieces of art because we want to show them to a large audience," said Sune Nordgren, director of the National Museum of Art in Oslo.
He said having armed guards would only result in thieves outgunning them.
In 2001, thieves raided neighboring Sweden's national museum and cut down a self portrait by Rembrandt and two paintings by Renoir. Those paintings were hanging from steel wires, like the paintings in the Munch museum.
Jan Birkehorn, head of security at the National Museum in Sweden, said it's almost impossible to make paintings theft-proof without ruining the experience for visitors.
"Should you put them inside security monitors with thick glass? I think the experience of looking at them would be lost," he said.
Museums tend to be tightlipped about security - talking about security "would be like giving an instruction manual to someone who wanted to steal something," said Clemence Goldberger of the Rodin Museum in Paris.
But Soili Sinisalo, director of the Finnish National Gallery's main art museum, the Ateneum, said her museum is retraining all 100-odd personnel in security and has placed cameras in each exhibit room.
"We are very aware of the changing world and the threats that face us, and therefore we have recently renewed all our security measures," Sinisalo said. "Security must be airtight. That's the only way to make sure that nothing is stolen."
In Spain, the major museums have armed private security guards and metal detectors at entrances. The staff keeps in contact through radios located on every floor and in every section.
"We had a series of measures that are visible to the public - but others that are secret," said spokesman Jose Maria Ambrona for Prado museum in Madrid.
The French Musee d'Orsay - home to great works by Renoir, Cezanne and Van Gogh - has extensive and largely secret security systems, in addition to guards and metal detectors.
But even that would not stop a violent robbery, such as the one in Oslo, said spokeswoman Nicole Richy.
"If an armed gang came into the museum with machine guns, there's not a lot that can be done," she said.
Laughing, she added: "the frames on the pieces in our museum are much heavier than those in the museum in Oslo, so they'd at least need more people to carry them away!"
Munch, a Norwegian painter and graphic artist who worked in Germany as well as his home country, developed an emotionally charged style that was of great importance in the birth of the 20th century Expressionist movement.
He painted "The Scream" in 1893, and together with "Madonna" it was a part of his "Frieze of Life" series, in which sickness, death, anxiety, and love are central themes. He died in 1944 at the age of 80.
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