The dense forests of southern Thailand and northern Malaysia have been a major stop-off point for smugglers bringing people to Southeast Asia by boat – most of them Rohingya Muslims fleeing persecution in Myanmar and squalid refugee camps in Bangladesh.

The discovery of camps and graves on the Thai side of the border in 2015 led authorities in Thailand to crack down on people smugglers, but prompted traffickers to abandon at sea thousands of migrants making their way to the border area in overcrowded boats.

Four people wanted in connection with the two countries’ probe into the camps discovered in 2015 were extradited from Thailand this week, and were expected to be charged on Friday at a sessions court in Malaysia’s northern Perlis state, Home Affairs Minister Saifuddin Nasution Ismail said in a statement on Thursday.

Saifuddin did not say what charges the four would face but stressed that Malaysia was “committed to maintaining border security and viewed issues of cross-border crime seriously, particularly human trafficking and migrant smuggling”.

The four people were among ten Thai nationals that Malaysia had sought for extradition since 2017 as part of its probe into the border camps, Saifuddin said.

Malaysia in 2019 launched a public inquiry into whether authorities mishandled an investigation into the 139 graves and more than 12 campsites suspected to have been run by people-smuggling groups.

The inquiry found weaknesses on the part of border patrols but concluded that no Malaysian enforcement officials, public servants or locals were involved in trafficking or migrant smuggling syndicates, according to a report published on the home affairs ministry’s website.

(Reporting by Rozanna Latiff; Editing by Kanupriya Kapoor)