A shipment of 18 human heads held up by customs officials at O’Hare International Airport was bound for a cremation service in the Chicago area after its use in medical research abroad.

A spokeswoman for the Cook County Medical Examiner’s Office, Mary Paleologos, said Tuesday that the heads were originally sent from Illinois to Italy for medical research and were returned to the area for disposal as part of the agreement.

She says a paperwork problem held up the shipment, which arrived at O’Hare in mid-December.

The containers were being stored at the Cook County morgue while authorities investigated the matter.

Paleologos says the heads will be turned over for cremation.