Federal agents arrested two Malaysian nationals in Oregon on accusations they smuggled orangutan skulls and parts of other wildlife into the U.S.

Authorities say the two were arrested Friday shortly after arriving in Portland to meet an associate. The criminal complaint says they own an online business that has been smuggling endangered wildlife into the U.S. since 2004.

The investigation began in 2013 when authorities found a helmeted hornbill mandible while searching an international package headed to Forest Grove, Oregon. Undercover agents then purchased three orangutan skulls, four helmeted hornbill skulls, a wild pig skull and other parts.

The two face charges of illegally importing wildlife into the U.S., which carries a maximum penalty of 20 years in federal prison and a $250,000 fine.