This agreement between Peru & Yale University for the return of artefacts could well form an outline for the handling of similar cases in the future.

From:
Yale University

Joint Statement by the Government of Peru and Yale University
FOR IMMEDIATE RELEASE: September 14, 2007

New Haven, Conn. — Representatives of the Government of Peru and of Yale University reached agreement today on a new conceptual framework for collaboration, with a focus on Machu Picchu. The relationship will embrace not only the archaeological materials Hiram Bingham excavated from Machu Picchu but also other aspects of scholarly and research interest, such as study of flora and fauna of the national park surrounding the archaeological site. Under the new framework, Yale and the Government of Peru will co sponsor an exhibition that will travel internationally, featuring objects from the Hiram Bingham expeditions in Cusco and Machu Picchu, dioramas and multimedia materials developed at Yale. The travelling exhibit will be curated by Yale and Peru’s National Institute of Culture scholars and will include additional pieces loaned by the Government of Peru.
The Government of Peru will undertake to build a new Museum and Research Center in Cusco, for which Yale will serve as advisor, and where the proposed exhibition will be installed following its tour.

It is intended that the international opening of the new Museum will coincide the centennial celebration of Bingham’s rediscovery of Machu Picchu.
Yale will acknowledge Peru’s title to all the excavated objects including the fragments, bones and specimens from Machu Picchu. In the spirit of collaboration, Peru will share with Yale rights in the research collection, part of which will remain at Yale as object of ongoing research. Once the Museum and Research Center is ready for operation in late 2009, the museum quality objects will return to Peru along with a portion of the research collection.
This understanding represents a new model of international cooperation providing for the collaborative stewardship of cultural and natural treasures.