The graves – mainly holding the remains of Rohingya refugees – were discovered in the jungle along the Malaysian-Thai border in 2015.
The men – aged between 30 and 58 – arrived in court in Kangar in Malaysia’s northern state of Perlis early on Friday morning, according to the Harian Metro newspaper.
The first of the mass graves – containing more than 30 bodies – was discovered in April 2015 among makeshift camps near the town of Wang Kelian that had been set up by traffickers bringing people across the border. After an intensified search, dozens more graves – many of them Rohingya refugees from Myanmar and containing more than one body – were found.
Thailand and Malaysia carried out a joint investigation into the camps, and Thailand convicted 62 defendants, including nine government officials, over the deaths and trafficking of Rohingya and Bangladeshis to Malaysia via Thailand in 2017.
Home Affairs Minister Saifuddin Nasution Ismail said the four Thais were extradited on Thursday and were among 10 people that Malaysia had sought for extradition in 2017.
In a statement on Thursday, he said Malaysia was “committed to maintaining border security and viewed issues of cross-border crime seriously, particularly human trafficking and migrant smuggling”.
Malaysia set up a Royal Commission of Inquiry (RCI) to investigate the tragedy in 2019, with 48 witnesses giving evidence.
The inquiry found that while no Malaysian enforcement officials, public servants or local citizens were involved in trafficking syndicates, there was “gross negligence” on the part of border patrols who had failed to notice the camps.
An independent report from Malaysia’s human rights commission (SUHAKAM) and Fortify Rights, found “reasonable grounds” to believe that a human trafficking syndicate committed crimes against humanity in Malaysia and Thailand against Rohingya men, women, and children from 2012 to 2015.
The report also highlighted how the syndicate deceived Rohingya, who come from Myanmar’s northwestern Rakhine state, to board ships bound for Thailand and Malaysia and abused them during the voyage.
Myanmar deprived Rohingya of their citizenship in a 1982 law, and amid escalating violence in Rakhine, many have tried to get to Malaysia, seen as a friendly majority Muslim country.
In 2017, hundreds of thousands of Rohingya fled across the border to Bangladesh amid a brutal military crackdown that is now the subject of a genocide investigation at the International Court of Justice.