AMSTERDAM -- The German task force investigating a huge trove of art recovered from a Munich apartment says one of the paintings - Henri Matisse's 1921 "Woman Sitting in an Armchair" - was looted from Jews by the Nazis and rightly belongs to the descendants of Paris art dealer Paul Rosenberg.

The painting depicts a dark-haired woman, seated with a fan in her lap and wearing a necklace and loose headscarf.

It was one of more than a thousand works found in the apartment of Cornelius Gurlitt, who inherited them from his father, art dealer Hildebrand Gurlitt, who was known to have worked with the Nazis.

The art was found in 2011 and became known to the public in in 2013. Cornelius Gurlitt died aged 81 in May, a month after agreeing to a deal with the German government under which the works he owned would be checked for Nazi-era links.

Initially, Gurlitt had insisted that all of the art belonged to him and nobody else.

"Even if it could not be documented with certainty under what circumstances Hildebrand Gurlitt came into the possession of the work, the task force comes to the conclusion that it is Nazi-looted art from the rightful property of the collection of Paul Rosenberg," said the task force's head, Ingeborg Berggreen-Merkel, in a statement.

Lawyer Chris Marinello, who represents the Rosenberg family, said heirs had not been informed of the task force's finding before Wednesday's announcement, and it is not completely clear the work will be returned - though he expects it eventually will.

Berggreen-Merkel said that in terms of restitution, the "final decision lies exclusively in the hands of the heir or legal successor of Cornelius Gurlitt." But at the same time, she noted that Gurlitt declared that he would abide by international agreements to return looted art before he died, and said in her opinion, "this obligation also binds his heirs."

Marinello said he has been frustrated by a lack of communication from the task force.

Wednesday's decision "continues the vein of disregard for due process and compassion that we have seen since the discovery of the Gurlitt hoard," he said.

"It is an unfortunate but entirely expected case of bureaucracy trumping empathy."

The Rosenberg family includes journalist Anne Sinclair, the ex-wife of former IMF chief Dominique Strauss-Kahn.