BANGKOK » Thai police issued arrest warrants Tuesday for two Americans who attempted to mail a preserved baby’s head, foot and other human body parts to the United States, saying the objects were stolen from a Thai medical museum.

The bizarre case has quickly gained international attention, with Thai police asking Cambodian authorities to help locate the men, who traveled to the neighboring country on Sunday, and the FBI helping with the investigation in the United States.

Police questioned Ryan McPherson, 31, and his friend, Daniel Tanner, 33, over the weekend in Bangkok, but released them and allowed them to travel to Cambodia. New elements then emerged after their departure, prompting the arrest warrants to be issued on charges of theft, possession of stolen items and falsely declaring items on shipping documents, said police Maj. Gen. Sombat Milintachinda, the head of Bangkok’s police investigation bureau.

"Our evidence indicates that they either stole the body parts, or they bought them from other people," he said. "We have to bring them back for more questioning."

It was apparently not the first brush with notoriety for McPherson and Tanner. Photos of the two talking with police on Sunday closely resemble men by the same names and ages who 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.

The "Bumfights" videos were banned in several communities and generally shunned by retailers after criticism that the films’ subjects were being exploited.

The case of the human body parts emerged over the weekend when parcel delivery company DHL said it scanned three U.S.-bound packages labeled as toys and detected five human body parts.

DHL alerted police who tracked down the senders, McPherson and Tanner, and brought them in for questioning. They told police they had bought the body parts at a Bangkok night market — an infant’s head, a baby’s foot sliced into three sections, an adult’s heart with a stab wound and two slices of tattooed skin. The objects were preserved separately in acrylic boxes with formaldehyde.

The men told police they thought the items were "bizarre" and "wanted to ship them to friends to surprise them," Sombat and other police said.

But new details surfaced Monday when one of Bangkok’s biggest hospitals, Siriraj Hospital, said the body parts were stolen from its anatomy museum and its forensic medicine museum — which the two men had visited last week.

Surveillance video showed the pair at the registration counters of both museums on Thursday, the same day police said they arrived in Thailand, said Udom Kachintorn, the medical dean at Siriraj Hospital.

The theft charge carries a jail term of one to five years or a fine of up to 10,000 baht ($300), while the false declaration charge carries a penalty of six months in jail and a 500,000 baht ($15,200) fine.

All three packages were being sent to Las Vegas, including one that McPherson had addressed to himself. Police said they contacted the FBI to get information about the would-be recipients of the items.

In Washington, FBI spokeswoman Minique Crump said it was aware of the matter and looking into it. In Las Vegas, FBI spokeswoman Bridget Pappas also said investigators were trying to determine whether laws were broken by the Americans.

Associated Press writer Eric Tucker in Washington contributed to this report.