A German recluse’s pledge to return his billion-dollar hoard of Nazi-looted artworks to their rightful owners was welcomed but also met with scepticism about whether all of it would actually be returned.

The legal custodian of Cornelius Gurlitt, who inherited the paintings drawings and sculptures from his father, said on Wednesday his client would return all works looted by the Nazis to their owners or owners’ descendants.

But the lawyer representing the heirs of Alfred Flechtheim, a Jewish art patron and collector who lost everything to the Nazis, questioned whether Gurlitt was in a position to make such a promise given that the art has been confiscated by the authorities.

“It remains to be seen … in which case this announcement actually leads to returns,” Markus Stoetzel told Reuters. “Gurlitt can make an announcement that he wants to return the art works but the prosecutor has to agree.”

Cornelius Gurlitt, the man whose modern art collection valued at RM4.5bil is under investigation for its connection with Nazi-looted art, on the cover of German publication Der Spiegel dated Nov 18, 2013 . Read the English version of the magazine's interview with Gurlitt