The captain of a Vietnamese oil tanker has been jailed for over five years in Singapore for his role in a scheme that saw around US$150 million of oil stolen from Shell’s biggest refinery over several years.

Doan Xuan Than, 47, was sentenced to 66 months in prison on Thursday, a spokesman for the State Courts of Singapore said, becoming the second person jailed in a case that also involves former employees of Royal Dutch Shell who allegedly conspired to siphon oil from the firm’s Singapore refinery.

The theft, which unfolded in the world's biggest ship refueling hub and Southeast Asia's petroleum refining hub, shone a spotlight on an illegal oil trade worth tens of billions of dollars worldwide

Than’s sentencing comes almost two years after Singaporean police raids that led to over a dozen arrests for alleged offenses dating back to 2014 in which around 340,000 metric tons of oil were filched from Shell’s refinery, which sits on an islet south of Singapore’s mainland.

Charge sheets seen by Reuters allege that Than was involved in the theft of gasoil from the Pulau Bukom refinery aboard vessels MT Gaea and Prime Sun on 10 occasions in 2016 and 2017. Than could not be reached for comment.

Another Vietnamese national was jailed for 2-1/2-years in July for related offenses, local newspaper Straits Times reported.

Besides the former Shell employees, there have been related charges filed against former employees of one of Singapore’s biggest marine fuel suppliers, Sentek Marine & Trading Pte Ltd; a Singaporean who worked for Intertek, a British-listed company specializing in quality and quantity assurance, including for fuel products; and other Vietnamese nationals who allegedly helped receive stolen property aboard ships.

Shell has previously said it was “disappointed” by what it uncovered at Pulau Bukom, was working closely with authorities and had implemented “measures to prevent this from happening again”.