Here is a more balanced article than what I have read elsewhere about the decision to withdraw an African mask from a Sotheby's sale. See
Although the press reported about on-line protests that preceded the decision see http://artsbeat.blogs.nytimes.com/2010/12/29/after-online-protest-sothebys-withdraws-african-mask-from-sale/?scp=1&sq=Benin%20Mask&st=cse, some additional context is necessary. The destruction of the Oron Museum and the wanton burning of hundreds of ancestral figures (ekpu) as firewood during and after the Biafran civil war certainly undercuts any Nigerian claim to the high moral ground. See Gathercole and Lowenthal, The Politics of the Past 297 (Unwin Hyman 1990). In short, any self-righteous indignation about 19th c. looting needs to be tempered by an acknowledgement of what Nigeria itself did to Oron culture in 1975.