According to The Guardian :
"The first anyone heard was a crash as the two armed robbers, masked in balaclavas, careered into plate glass doors at the front of the Munch Museum. In their adrenalin-psyched eagerness to snatch one of the most renowned and valuable of modern paintings, the gang reportedly misjudged the gallery's sequence of automatic sliding doors. But the blundering entrance - which startled Sunday morning tourists drifting through the gallery and alerted security guards - was followed by a rapidly executed theft."
