Department of State Involved in Illegal Antiquities Trade?

British antiquities expert John Howland states that

government officials and/or departments connive with bent archaeologists to have valuable artefacts popped into Diplomatic Bags (contrary to international conventions) to evade import and Customs' controls. It has happened before and is probably a widespread practice and not solely the preserve of crooked British archaeologists out for an easy buck.

But of course it is not just British archeologists that work in most of the source countries for items on our market. There is a US archeological presence in most countries with ancient civilizations and in most of them is also a US embassy or consulate. Are diplomatic pouches sent by the staff of the Office of Foreign Missions the means by which many illegal artefacts are entering the market and evading the import controls imposed by the Bureau of Educational and Cultural Affairs? It would be ironic if the one was trying to deprive collectors of these items, but within the same government Department was an established network keeping the trade alive with government approval.