The company, DHL, alerted police who tracked down the sender, a 31-year-old American tourist who said he found the items at a Bangkok night market, police Col. Chumpol Poompuang said.
"He said he thought the body parts were bizarre and wanted to send them to his friends in the U.S.," Chumpol said, adding that the man was questioned for several hours and released without charges.
The three packages, which contained five body pieces, were labeled as toys, police said. They were being sent to Las Vegas, including one parcel that the man had addressed to himself.
Chumpol had earlier said a baby's heart and intestines were among the body parts. But police at a news conference later in the day said the heart, which had been stabbed, was from an adult and there were no preserved intestines.
Police Lt. Gen. Ruangsak Jarit-ake told reporters that all the parts were preserved separately in formaldehyde inside sealed acrylic or plastic boxes. He displayed graphic pictures of all five body parts, which also included two pieces of tattooed skin from an adult - one with a jumping tiger and the other bearing an ancient Asian script. A close-up picture of the baby's foot showed that it had been sliced into three sections.
The method of preservation and the manner in which the parts were cut appeared to be professional and authorities were investigating if the parts were stolen from medical institutes.
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.
In 2012, a British citizen was arrested with six roasted fetuses covered in gold leaf after a tip-off that infant bodies were being sold through a website offering black magic service.
- THANYARAT DOKSONE
Associated Press writer Jocelyn Gecker contributed to this report.