Over 1,500 Nazi-stolen modern paintings — from artists like Picasso, Matisse and Chagall — were found in a Munich apartment during a tax-related raid back in 2011, the German magazine Focus reports.

The items, valued at $1.3 billion, were discovered when tax authorities searched the home of Cornelius Gurlitt, the son of a Munich art dealer, who was suspected of tax evasion. Gurlitt is said to have kept the art work in a dark room and sold paintings from time to time when he needed the money.

Some of the pieces were deemed degenerate by the Nazis and others were stolen or forcibly sold at a low price by Jewish art collectors back in the 1930s and 1940s. According to the U.S. Holocaust Memorial Museum, the Nazis seized a total of 16,000 art pieces during the war.

The stolen collection is being held in a secure warehouse in Munich for the time being.