On trial are dozens of suspects, including military, police and government officials, accused of trafficking people, many of them Muslim Rohingya and Bangladeshis.
More than a hundred detainees appeared in Bangkok's main criminal court on Tuesday for the opening of their defence on an array of human trafficking charges.
Thailand has long been a major hub for human trafficking and people smuggling. Authorities have been accused of turning a blind eye and even of complicity.
The Thai government launched a crackdown on the lucrative business in 2015 and arrested dozens after mass graves were found on the Thai-Malaysia border.
Tuesday's proceedings were the continuation of a trial prosecutors launched in March 2016.
The defendants include a senior army general, a police officer and government officials. All have pleaded not guilty to offences that include smuggling, kidnapping and involvement in the deaths of dozens of people found in the shallow graves.
Many of the victims were Rohingya and Bangladeshis, who were corralled in jungle camps on the Thai-Malaysia border. In cases they were beaten or raped until relatives paid a ransom.
TRT World's Tazkira Sattar in Bangkok has this story on one of the victims.