UDD lawyer Karom Phonpornklang led UDD members Prompong Plangklang and Chamnan Tohchaeng, both 45 and Nakhon Ratchasima natives, to DSI headquarters.
In their complaint, Mr Prompong and Mr Chamnan said they were wounded by gunfire while serving as volunteer security guards for the Red Shirt demonstrators during the 2010 political unrest in Bangkok. Ninety-one persons died during the March-May politically-related violence.
The two men said they were wounded on April 10 as demonstrators clashed with government security personnel at Din Sor Road near Ratchadamnoen Avenue.
The complainants said they wanted legal action to be taken against those who authorised the shootings for attempted murder. They had prepared medical certificates and police reports to accompany their petitions.
Mr Abhisit and Mr Suthep on appeared December 14 at the DSI to hear charges but they rejected all allegations laid against them and vowed to contest all charges against them without compromising or fleeing the country.
The DSI charged them with authorising the shooting of demonstrators during the political protest and suppression by military units under the now-expired Centre for the Resolution of the Emergency Situation (CRES).
Mr Suthep was then CRES director while Mr Abhisit was implicated in the murder allegations in his capacity as prime minister overseeing the emergency centre.