London market and the American collector: pieces to return to Egypt

It is being reported that four fragments from the mortuary temple of Amenhotep III are to be returned to Egypt (Mohamed Azouz, "Egypt to receive four stolen artifacts from the UK within days", Almasry Alyoum August 6, 2011). They were seized when their present proprietor, a North American private collector, consigned them to a London auction house.

The pieces had been removed from the base of an ancient statue of Amnehotep III in his mortuary temple in Luxor, the statement said. It added that three are heads with Asian features and the fourth is a cartouche that belonged to the pharaoh.

The items were apparently spotted by a Trustee of the British Museum.

Who was the collector? How had (s)he acquired them? Which auction house was due to sell them? What had the due diligence search revealed?

We should note that an eye from a statue in the same complex was returned from Switzerland in 2008.