A Burmese drug trafficker notorious in Southeast Asia’s illicit opium producing-region, known as the “Golden Triangle” has been found guilty of murdering 13 Chinese sailors, the Asahi Shimbun reports.

Naw Kham, who was extradited to China by Laos in May, and five gang members were found guilty of charges including intentional homicide, drug trafficking, kidnapping and hijacking by the Intermediate People’s Court of Kunming in southwest China. Two Chinese cargo ships with 13 sailors aboard were hijacked in October while traversing the Mekong River which stretches from China to Southeast Asia where it goes between Myanmar and Laos then Thailand and Laos. The sailors were executed and tossed overboard inside Thai territory, according to investigations.

Naw Kham denied that he was the gang’s leader but the five members contested his statement. “Prosecutors showed irrefutable and sufficient evidence of criminal offenses, including the six defendants’ confessions, witness testimonies, DNA test results, and autopsy reports,” the court stated. The court still hasn’t announced a date for the sentencing.

Chinese media Xinhua news agency said that Naw Kham “expressed his penitence to the victims and their families” and was “hoping for leniency”. The case is part of Beijing’s attempt to bolster its role in regional security, Reuters reports.