German authorities are investigating a group of art forgers responsible for a multi-million-dollar art scam with victims that include actor Steve Martin.

Art experts, Christie's auction house, reputable Parisian galleries, and collectors were duped by the fake paintings with fabricated provenances slowly seeped into the market by the art forgery ring, possibly since the 1990s.

Martin had purchased a bright landscape by German Expressionist painter Heinrich Campendonk from Parisian gallery Cazeau-Béraudière, for €700,000 ($850,000) in 2004. He later sold it at Christie's for a loss.

Now Martin's previously-owned painting has been deemed a fake, one of as many as 30 forgeries of early modernist painters such as Fernand Léger and Max Ernst produced by the forgers.

The total losses are estimated at €34.1 million ($48.6 million) so far.