Police have arrested 75 people in connection with a massive human-trafficking ring, which allegedly smuggles Chinese migrants into Europe and the United States, the Spanish Interior Ministry confirmed Saturday.

Fifty-one people were arrested in Spain and 24 in France, the Global Post reports. The gang, whose main office is in China, has been under investigation since 2011.

Spain reportedly served as a “travel springboard,” according to Euro News. Most of the captives would eventually end up in Great Britain or the U.S.

Spanish police found 81 fake passports from countries including Taiwan, South Korea, Malaysia, Japan, Hong Kong and Singapore along with document-forging equipment, such as portable computers, scanners, 20 fake customs stamps and an electronic magnifier.

The crime ring reportedly charged approximately $66,000 to forge documents and transport the Chinese migrants via Barcelona airport to their destinations. Barcelona served as a stopping-off point, where the migrants were held while the false documents were prepared, according to the Huffington Post.

The gang also has links to a prostitution ring, leading authorities to believe that some of the migrant workers were sexually exploited.