Between 40 and 60 human heads were found in a cargo shipment by a Southwest Airlines employee last week, the airline confirmed Thursday. The heads, which were intercepted in Little Rock, Ark., were promptly handed over to local officials, who are now investigating whether the body parts were legally obtained and handled.

Southwest officials said the airline refused to ship the package because it was not labelled correctly. "And then when we found out what was in the package, we contacted local authorities and they contacted the coroner," said airline spokesman Marilee McInnish.

The package was on its way to the Fort Worth office of Medtronic, a Minnesota-based medical research and technology company, NBC's affiliate in Dallas Fort-Worth reported. Little Rock police handed the package over to the county coroner. The coroner is currently investigating whether the human specimens were legally obtained.

"We are investigating to make sure that this isn't an illegal process that is going on," Pulaski County coroner Garland Camper said. "If these specimens are being obtained illegally and are for a purpose other than medical research, or maybe some type of underhanded blackmarket scheme, we want to make sure that is not happening."

McInnish said it was her understanding that the heads were going to be used for educational and research purposes, although Camper said that fact has not been verified and is still under revue.

Federal law prohibits the sale of body parts. Suppliers of the parts, however, can be reimbursed when those parts are used for legitimate medical education and research.

A Medtronic spokesman told NBC that JLS Consulting LLC, based in Conway, Ark., was the supplier of the heads in this instance. The founder of JLS told the Arkansas Democrat-Gazette that nothing was wrong and that her company was providing authorities with the proper documentation. Camper said the Little Rock coroner's office is still investigating the company.

A Southwest spokesman said the airline is now working to educate the parties involved in the shipment on proper protocol for body-part shipments in the future.