The customs office at Chicago’s O’Hare International Airport was temporarily held up on Tuesday for what officials nonchalantly described called “not an unheard of delivery” -- a shipment of 18 severed human heads.

According to Mary Paleologos, a spokeswoman for the Cook County Medical Examiner’s Office, the heads came from a legitimate facility in Rome and were shipped to Chicago in mid-December. Paleologos added that the heads have been designated for anatomical research purposes, and were properly sealed and frozen in containers and appropriately marked as human specimens. She added that there was nothing to suggest there had been foul play.

Customs officials at the Chicago airport said that the shipment was prevented from being dispatched to its final destination due to a paperwork problem, but the Sun-Times reported that the halt was related to an ongoing investigation at the facility where the heads were due to arrive. The publication’s source added that the investigation was “absolutely not” related to the heads.

Brian Bell, a spokesman with the U.S. Department of Homeland Security, said that the heads appeared to be in order and suggested that nothing was amiss.

“There’s no issue with the transportation of body parts for medical purposes,” said Bell. “There’s nothing against the law that says you cannot ship them, provided you have the right documentation.”

He added that although the incident marked the first time he was part of an investigation into such a shipment, he said they were not altogether uncommon.

“Everybody here is ‘Oh my gosh, you got a box of heads’ and everybody thinks that it’s unheard of,” Bell said. “It is a potentially legitimate medical shipment. We’ve seen it at various ports in the nation.”

“We need to make sure that they are truly used for medical research purposes,” said Bell.

He added that the job of customs officials is simply to confirm that the heads are indeed designated for use as medical specimens, and that until then they will remain at the Cook County’s morgue.