Mr Sithithat reportedly said he began writing the anti-National Council for Peace and Order leaflets around 7pm Saturday night and finished printing them about 3am Nov 23.
Police said he admitted putting a bag containing the leaflets in the boot of his car and drove to Soi Samranrat where he gave the bag to Mr Wachira. It was Mr Wachira who took the bag on his motorcycle and dropped the leaflets around the Democracy Monument at about 5am, police said.
Mr Sithithat also is said to have admitted joining the PDRC protests on Ratchdamnern Avenue to gather information, explaining why he had PDRC shirts in his possession.
Col Kachachart said Mr Sithithat would be charged for violating martial law and might have to stand trial in military court.