Checking of Sources of Antiquities on the London Market?

Roberta Mazza [From Egypt to London: looting in Antinoupolis (el Sheikh ‘Abadah) March 27, 2015] reports the content of an Analecta Papyrologica article by Rosario Pintaudi et al (Pintaudi, Rosario ; Silvano, Flora ; Del Corso, Lucio ; Delattre, Alain ; Spanu, Marcello “Latrones: furti e recuperi da Antinoupolis”, Analecta Papyrologica XXVI 2014 pp. 359-402) discussing illegal excavations and looting in the area of Antinoupolis. The text includes the information about a

Roman glass inlay stolen from the excavation site and later found on sale in an auction catalogue. This little and beautiful piece traveled from Egypt to the showrooms of Bonhams in London, where the sale was stopped by the police, after the object sold for about £ 5,000. [...] As often happens, in the auction catalogue provenance was recorded as “English private collection, acquired in the late 1960s.”

I am not clear whether this meant that the inlay came from illicit and clandestine digging of unexcavated layers of the excavation site, or whether this was an excavated object (and therefore in the site documentation) which was recently stolen from the stores. I presume that the fact that the sale (which took place in October 2013) is reported as cancelled would indicate the latter. Did any prosecutions result from this? In any case, how did Bonhams verify the claim they published in their sales catalogue?

UPDATE Mar 28th 2015.

'Mosaic glass: from Antinoupolis to London', Looting Matters Saturday, March 28, 2015