United Front for Democracy against Dictatorship (UDD) core member Jatuporn Prompan claimed on Wednesday he had new evidence about the "men in black".
Mr Jatuporn was speaking after submitting to the Department of Special Investigation (DSI) a copy of a Civil Court verdict on a case involving the protest in which the army was ordered to pay compensation to a victim. Use of live ammunition in military operations to quell the riots was mentioned in the verdict.
He also handed over to the DSI photos and documents he said contained information on the CentralWorld fire.
Mr Jatuporn said he believed the photos of "men in black" shown by the Centre for the Resolution of the Emergency Situation (CRES) were made up.
The facts surrounding the "men in black" had yet to be clearly established, he said, adding that he had found new evidence.
The evidence was photos of "men in black" mingling with soldiers at many military positions during the 2010 UDD protests.
On the day Maj-Gen Khattiya Sawasdipol, or Seh Daeng, was shot, some "men in black" followed Seh Daeng while he was being rushed to Hua Chiew Hospital for treatment, he said.
Mr Jatuporn said the story of the "men in black" had been plotted in advance by the previous government.
"(Former prime minister) Abhisit declared the emergency decree despite the fact that there had not been any acts of terrorism. This was followed by the military operation at Khok Wua intersection and Si Ayutthaya Road.
"I believe the Democrat Party tried to fabricate the "men in black" story even though nobody had seen their faces," Mr Jatuporn said.