Paris: A sketchbook that belonged to Pablo Picasso and is worth several million euros has been stolen from a Paris museum after the case containing it was left unlocked, police and museum staff said on Tuesday.

The theft at the Picasso Museum in the heart of Paris occurred overnight but there was no sign the building had been broken into, police said.”The lock of the display cabinet was not closed because it was broken,” a museum employee said, adding that the artist’s sketchbook was on display in a place that was difficult to monitor.

The sketchbook was valued at 7-10 million euros ($9.7 million-$13.9 million) but the museum employee said it was insured for 125 million euros.