Ulrich Boser, who wrote the book on the Gardner Museum art theft, explains in the Wall Street Journal why museum security is so lax, as it was in Paris:

To be sure, security is expensive. A full roster of guards can eat up half of a museum’s operating budget—and that doesn’t include the cost of high-tech motion detectors and electronic keys. A small institution can spend more than $1 million a year on security services. The Smithsonian in Washington, D.C. pays out almost $70 million annually to protect its collection, and even that might not be enough. A 2007 government report found that the Smithsonian did not have enough guards to respond to alarms, and someone had managed to sneak some mammalian fossils out of one of the galleries.

Museums also suffer from an art-security Catch-22: By making it easy for the public to experience great art, they make it easier for crooks to steal it. And when institutions don’t provide an intimate, nose-to-the-canvas environment, visitors complain. When thieves pilfered Edvard Munch’s masterwork “The Scream,” they left behind a note that said “Thanks for the poor security.” After the heist, the Munch Museum in Oslo turned their institution into an art-world Fort Knox, with metal detectors and an X-ray machine. The press dubbed the building Fortress Munch, and some art-lovers grumbled, saying that they couldn’t appreciate the masterpieces because of the thick, protective glass.

This is No ‘Thomas Crown’ Affair (Wall Street Journal)