The Customs & Excise Department has prosecuted a cross-boundary smuggling syndicate, through the first-ever evidence-taking hearing on the Mainland.

The successful hearing led to five syndicate members being jailed for up to six years today.

Hong Kong and Mainland customs officers launched an investigation into the syndicate, after it was believed to be smuggling more than 500,000 tonnes of marked oil by fishing vessels to the Mainland, and laundering crime proceeds of up to $2.6 billion in recent years.

In a joint crackdown in 2010, the department arrested 19 people, including the gang's masterminds, and froze $240 million worth of crime proceeds. Five people were prosecuted in August 2010.

The department identified four Mainland witnesses who had information crucial to the prosecution. To obtain the evidence, for the first time it sought help from the Mainland court with the assistance of the Department of Justice and the Judiciary.

From May to September last year, with the co-ordination of Mainland customs officials, the department, together with a District Court Judge, and prosecution and defence counsels, attended an evidence-taking hearing at Shenzhen Municipal Intermediate People's Court.

Testimonies were obtained from the four witnesses and were later ruled admissible as evidence.

The case was tried at the District Court from August to November. The five defendants were convicted of conspiracy to export unmanifested cargo, and money laundering charges.

The department will also apply to confiscate the $240 million in crime proceeds.