Investigators have uncovered Germany's largest-ever illegal value-added tax (VAT) evasion scheme, the Berlin State Prosecution Office has announced.

The prosecutors said on Wednesday night that more than 50 individual suspects and firms stand accused of having withheld several hundreds of millions of euros in VAT from fiscal authorities in revenue generated through copper trading activities.

At least 100,000 tons of the commodity are believed to have been brought to Germany from Serbia where it was then sold illicitly to industrial customers via a network of front companies.

A 47-year-old Bosnian citizen has already been sentenced to seven years in prison by the Berlin Higher Regional Court as the ringleader behind the VAT evasion scheme. The individual has appealed the decision and is currently not in police custody.

Martin Steltner, a spokesperson for the Berlin State Prosecution Office, told press on Wednesday that investigations were first launched in 2014 and have led to the confiscation of 25 million euros (28.4 million U.S. dollar) in assets so far. The case was not revealed to the public until now in order to enable investigators to carry out their covert work without potential disruptions.