A total of 71 paintings by renowned Austrian artists such as Oskar Kokoschka, Emil Beischläger and Alfons Walde were stolen from a private villa in the Austrian capital Vienna, Der Standard reported. The works are valued at over €2 million.

A 73-year-old former professor returned home from a 10 day vacation to find that the walls of her home had been stripped bare by thieves who had stolen her entire art collection.

Police spokesman Thomas Keiblinger confirmed earlier news reports to the paper that the crime was committed between the 21st and 31st of August. The police believe the heist was the work of experienced art thieves.

The robbers were able to commit the crime undetected by turning off the alarm and entering the villa from the rear. Police believe they left the scene with the paintings in the back of a truck. “They were professionals. They knew how and what they stole,” Keiblinger told The Local.

So far, no witnesses have come forward. However, forensics experts were able to secure some evidence form the scene, including DNA samples. At the time of writing, those had yet to produce any leads as to who may be responsible for the crime.

The Austrian Federal Criminal Police have circulated photos of all the stolen paintings online and are appealing to the public to come forward with information.