The announcement comes just weeks before the expiry of the statute of limitations of the case on Oct. 25 and follows a related complaint against seven former senior security personnel filed by the victims' families that a court accepted last month.
Only one individual has been named in both cases.
"The suspects could have foreseen that their actions would have led to the suffocation and deaths of the 78 people under their responsibility," attorney-general spokesperson Prayut Bejaguran told a press conference.
The cases are centred around a high-profile incident in the town of Tak Bai in the southern province of Narathiwat in 2004, when seven protesters were killed by gunfire and 78 more were crushed or suffocated to death while piled on top each other in army trucks.
Thailand's government at the time expressed regret at the Tak Bai deaths but denied wrongdoing, while police had initially said some protesters were armed.
The crackdown, which drew international condemnation, occurred during martial law and was one of the deadliest incidents during a separatist insurgency that reemerged that same year and has since killed more than 7,600 people in Thailand's predominantly Muslim provinces near Malaysia.
The incident took place under the administration of former Prime Minister Thaksin Shinawatra whose daughter, Paetongtarn Shinawatra, became premier last month.
Last week, a Narathiwat court summoned a former military commander and issued arrest warrants for six retired senior security personnel after they failed to appear at a criminal hearing over the complaint filed by the families.
