The Collection of Liberia's National Museum: Smuggled to the US?

From a brief news item from The News, published on allafrica.com:

More than 5,800 pieces of arts and artifacts went missing from the National Museum during Liberia's 14-year civil conflict, the Director of the Museum Albert S. Markeh has revealed. 

He claimed that most of these materials were looted and smuggled to neighboring countries, while some have surfaced in the African-American and Masonic Museums in the United States of America and other parts of the world. 

Mr. Markeh expressed fear that retrieving these artifacts could be challenging for the National Museum because Liberia has no treaty that empowers Museum authorities to engage the American to retrieve the items. 

Director Markeh, however, explained that in the absence of a treaty, the missing artifacts could be retrieved through diplomatic channels, and hoped that the Liberian Government will see the need to engage United States authorities over this issue. 

Meanwhile, National Museum Director has indicated that unless something is done urgently to rehabilitate the National Museum building on Broad Street, it will collapse.
He said the building currently housing the National Museum on Broad Street is fast declining, having being built in 1862 and has not undergone major renovation.

While there's no question that the National Museum and its collection of historical artifacts was decimated during the War, the assertion here that these items were illicitly passed to American museums, which still hold on to them is new: