(Jacques Brinon ~ Associated Press)
The paintings disappeared early Thursday from the Paris Museum of Modern Art, across the Seine River from the Eiffel Tower in one of the French capital's most tourist-frequented neighborhoods.
The museum's alarm system had been broken since March 30 in some rooms, Paris Mayor Bertrand Delanoe said in a statement. The security system operator ordered spare parts to fix it but had not yet received the equipment from the supplier, the statement said.
The museum reopened in 2006 after spending 15 million euros and three years upgrading its security system.
Christophe Girard, deputy culture secretary at Paris City Hall, said a single masked intruder was caught on a video surveillance camera.
Investigators are trying to determine whether the intruder was operating alone, Girard told reporters, who suggested the heist was carried out by a very "sophisticated" team or individual. He said three guards were on duty overnight, but "they saw nothing."
The intruder entered by cutting a padlock on a gate and breaking a museum window, the Paris prosecutor's office said.
The prosecutor's office initially estimated the paintings' total worth at as much as $613 million but later downgraded that to $112 million. Girard said the total value was "just under 100 million euros."
He said "Le pigeon aux petits-pois" ("The Pigeon with the Peas") a Cubist oil painting by Pablo Picasso, was worth an estimated 23 million euros, and "La Pastorale" ("Pastoral"), an oil painting of nudes on a hillside by Henri Matisse about 15 million euros.
The other paintings stolen were "L'olivier pres de l'Estaque" ("Olive Tree near Estaque") by Georges Braque; "La femme a l'eventail" ("Woman with a Fan") by Amedeo Modigliani; and "Nature morte aux chandeliers" ("Still Life with Chandeliers") by Fernand Leger.
Alice Farren-Bradley of the Art Loss Registry in London said the Paris theft "appears to be one of the biggest" art heists ever, considering the estimated value, the prominence of the artists and the high profile of the museum.
She added, however, that the value of the paintings would have to be confirmed, as museums and art dealers often value paintings differently.
She said it will be "virtually impossible" to sell such prominent paintings on the open market and that typically stolen art fetches lower prices on the black market.
"Very often they can be used as collateral to broker other deals" involving drugs or weapons, she said. "They are not necessarily going to be bought by some great lover of the arts."
While the thefts are often carefully planned, that's not always the case for the next step -- selling the stolen paintings -- which is why they are often recovered, she said.
Interpol is alerting its national bureaus around the world to the theft.
"This is a big theft, that is very clear," Stephane Thefo, a specialist at Interpol who handles international art theft investigation, told The Associated Press. "These works are of an inestimable value."
He expressed doubt that one person could have pulled off the theft alone, even if only one person was caught on camera.
Red-and-white tape surrounded the museum, and paper signs on the museum doors said it was closed for technical reasons.
On a cordoned-off balcony behind the museum, police in blue gloves and face masks examined the broken window and empty frames. The paintings appeared to have been carefully removed from the disassembled frames, not sliced out.
A security guard at the museum said the paintings were discovered missing by a night watchman just before 7 a.m. (0500 GMT, 1 a.m. Thursday EDT). The guard was not authorized to be publicly named because of museum policy.
Paris Mayor Bertrand Delanoe said in a statement that he was "saddened and shocked by this theft, which is an intolerable attack on Paris' universal cultural heritage."
The director of the neighboring modern art museum Palais de Tokyo, Pierre Cornette de Saint-Cyr, called the thief or thieves "fools."
"You cannot do anything with these paintings. All countries in the world are aware, and no collector is stupid enough to buy a painting that, one, he can't show to other collectors, and two, risks sending him to prison," he said on LCI television.
"In general, you find these paintings," he said. "These five paintings are unsellable, so thieves, sirs, you are imbeciles, now return them."
Flemming Friborg, manager of Copenhagen's Glyptotek museum -- known for its Impressionist paintings, among others -- called the theft of the high-caliber paintings "like the death of a family member."
Associated Press writers Christina Okello, Greg Keller and Nicolas Garriga in Paris and Karl Ritter in Stockholm and Jan M. Olsen in Copenhagen contributed to this report.