A Singaporean businessman wanted by the U.S. for helping smuggle oil into North Korea has been in Singapore since early last year, the city-state’s police force said Friday evening, just one day after the U.S. offered $5 million for information on the alleged sanctions violator.

According to a Singapore Police Force (SPF) press release, authorities seized Kwek Kee Seng’s passport in April last year after the U.S. first brought a criminal complaint against him. He has been under investigation ever since, though it’s unclear if Kwek is in custody.