Not until 1998, when 44 nations including the United States signed the groundbreaking Washington Principles on Nazi-Confiscated Art, did governments and museums formally embrace the idea that they have a special responsibility to repair the damage caused by the wholesale looting of art owned by Jews during the Third Reich’s reign.

Now, 15 years later, historians, legal experts and Jewish groups say that some American museums have backtracked on their pledge to settle Holocaust recovery claims on the merits, and have resorted instead to legal and other tactics to block survivors or their heirs from pursuing claims.

In recent years judges have dismissed several cases after museums argued that recovery claims had been filed too late. California legislators were so disturbed by one blocked claim there that they passed a law in 2010 to help Nazi-era (and other) claimants avoid tripping over legal deadlines.

In some of the cases, museums like the Detroit Institute of Arts, the Toledo Museum of Art in Ohio, the Museum of Fine Arts in Boston and the Solomon R. Guggenheim Museum have tried to deter claimants from filing suit by beating them to the courthouse and asking judges to declare the museums the rightful owners.