Police in Thailand have issued arrest warrants for two Americans they say stole human body parts from a local medical museum and attempted to mail them to the United States. 

Police on Tuesday issued the warrants for Ryan McPherson, 31, and Daniel Tanner, 33 on charges of theft, possessing stolen items and falsely declaring the items on shipping documents.

The pair left Thailand on Sunday for neighboring Cambodia after police questioned and released them without charges. They told police they had bought the items at a Bangkok night market. They described the items as toys on shipping documents.

On Monday, a major Bangkok hospital said the objects were stolen from two of its museums, which the men had visited last Thursday. Clinical Professor Udom Kachintorn, the dean of the Faculty of Medicine at Bangkok's Siriraj Hospital, told reporters that the five human body parts were stolen from the hospital's museums. Two of them belonged to the department of anatomy and the other three to the department of forensic medicine.

He said the two Americans visited the museum last Thursday, but that closed-circuit television video did not show them taking any items away.

Police Col. Chumpol Poompuang said McPherson had initially been tracked down after the shipping company, DHL, alerted authorities to the actual contents of the shipment, which included a preserved baby's head and foot. 

"He said he thought the body parts were bizarre and wanted to send them to his friends in the U.S.," Chumpol said. The three packages seized in Bangkok were being sent to Las Vegas, including one parcel that McPherson had addressed to himself. Police said they were contacting the FBI to get information about the would-be recipients of the items.

In Washington, spokeswoman Minique Crump said the FBI was aware of the matter and was looking into it.

Police Lt. Gen. Ruangsak Jarit-ake displayed graphic pictures of the five body parts and told reporters that the parts had been preserved separately in formaldehyde inside sealed acrylic or plastic boxes. Two of the parts were pieces of tattooed adult skin — one with a jumping tiger and the other bearing an ancient Asian script.

In some Thai cults, preserved fetuses or spiritual tattoos are believed to give the owners good fortune or protection from evil. They can also be used to practice black magic.

McPherson and Tanner were producers over a decade ago of a video series featuring homeless people brawling and performing dangerous stunts after being paid by the filmmakers, who were based in Las Vegas.

They claimed sales of about 300,000 copies at $20 each, though their "Bumfights" videos were banned in several communities and generally shunned by retailers after criticism that the films' subjects were being exploited.

In 2002, the district attorney's office in San Diego, Calif., filed felony charges including battery against McPherson and Tanner and two others in connection with production of the "Bumfights" videos. A judge reduced the counts to misdemeanors and the four pleaded guilty in 2003 to arranging a fight without a permit. They were fined $500 each and ordered to perform community service at a homeless shelter, but McPherson and one colleague were sentenced to 180 days in jail in 2005 for failing to complete their community service.

The Associated Press contributed to this report.