The provincial court invoked Article 90 of the Criminal Code for punishment on arson attack at a government installation.
Of the 29 defendants, 16 were acquitted due to lack of evidence.
Following the dispersal of Ratchaprasong rally on May 19, 2010 in Bangkok, red shirts in Mukdahan stormed and torched their provincial hall.
The defence is expected to appeal the decision in 30 days.