Story highlights If convicted, the two Americans could face 7 years in prison or be fined $15,200

The two suspects have left Thailand and are now in Cambodia

Thai police are contacting Interpol and Cambodian police to try to trace them

Officials: The body parts were stolen from a hospital; video shows the two Americans

Arrest warrants have been issued for two Americans accused of stealing adult and infant body parts from a museum inside a Thai hospital and trying to ship them to Las Vegas.

But the two men have already left Thailand despite being interviewed by police.

The Americans, Ryan Edward McPherson and Daniel Jamon Tanner, told police they wanted to surprise their friends back home, Royal Thai Police Deputy Commissioner Gen. Ruangsak Jritake said Monday.

It's unclear whether McPherson or Tanner have attorneys. So far, they have not able to be reached for comment.

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A delivery company uncovered the macabre shipment. On Saturday, a DHL office in Thailand's Pathum Thani province called police after workers there were scanning shipments and discovered the body parts inside three packages.

The packages contained five acrylic plastic boxes, Ruangsak said.

One box contained an infant's head; another contained a baby's left foot, which was sliced into three pieces, the police official said. The other acrylic boxes contained an adult heart and adult skin.

Flea market claim

Over the weekend, police said they had talked to an American who was trying to send the parcels to the United States but couldn't bring any charges against him because they weren't sure what laws applied to the case.

At the time, police said the American told them he found the infant body parts at a night flea market and that he had paid about $100 for them -- though he could not remember where the market was located.

But on Monday, authorities revealed more details on the case.

All the body parts were stolen from the Siriraj Medical Museum within Bangkok's Siriraj Hospital, the largest hospital in Thailand, Ruangsak said. The body parts were taken from the forensic medicine museum and anatomical museum.

Police said closed-circuit video from the hospital showed two men identified as McPherson and Tanner.

"The two foreigners definitely visited our museum, but we cannot see from the CCTV camera that they stole those items," said Udom Kachintorn, dean of the hospital's faculty of medicine. "It is evidence that confirms the two foreigners are linked to the missing items."

Police said they were also investigating whether museum employees or other local people were involved in the theft.

Arrest warrants issued

A Thai criminal court approved arrest warrants for the two men on charges of theft from a government hospital, as well as breaching customs law, police said Tuesday.

If convicted, McPherson and Tanner could face up to seven years in prison or a fine of up to 500,000 Thai baht ($15,200).

But the Americans have already left Thailand for Cambodia. Thai police said they would send the arrest warrants to the Bangkok office of Interpol, the international police agency, to try to trace the men.

They also said they were in touch with Cambodian police directly and had asked the FBI, through the U.S. Embassy in Bangkok, to gather information on the packages' destinations.

Officials at the U.S. embassies in Thailand and Cambodia said they were aware of reports about the case but couldn't comment, citing privacy concerns.

Black market for body parts

The bizarre discovery is not the first time infant remains have been found in Thailand. In 2010, more than 2,000 illegally aborted fetuses were recovered at a Buddhist temple in Bangkok.

Infant body parts can be bought on the Thai black market. Some Thais practice black magic and believe that supernatural power comes from infant body parts, if the rites are performed by monks or sorcerers. They believe that having the items provides protection and business success and can ward off bad luck.

In 2010, police said the smell of decay led investigators to the Phai-nguern Chotinaram temple in central Bangkok, where they discovered more than 2,000 illegally aborted fetuses . Three people were arrested, including two morticians who were charged with hiding bodies.