Vivat Yodprasit, who was dubbed by media the popcorn gunman, was released on Thursday after serving less than six years in jail for his role in a shoot-out in Bangkok's Laksi district in 2014 that killed one person and wounded three others during street demonstrations.
He was sentenced by the Criminal Court in March 2016 to 33 years and four months for collaborating to commit murder and another four years for carrying firearms in public in regard to the shooting on the eve of the Feb 2, 2014 snap election.
He was originally sentenced to life in prison but this was later reduced following a confession.
The Appeal Court acquitted him of the charges in 2017, giving him the benefit of the doubt due to insufficient evidence proving he was the gunman. However, he remained in jail pending an appeal in the Supreme Court which in 2018 stood by the 37-year-and-four-month sentence given by the Criminal Court.
He was originally arrested in March 2014 at a market in Surat Thani's Muang district. Since being indicted, Mr Vivat had never been granted bail and was detained at Khlong Prem prison in Bangkok.
Mr Vivat earned the title "popcorn gunman" because photographs in the media showed a masked man firing off rounds from an assault rifle hidden inside a bag of popcorn during the clash.
Four people were struck by bullets.
One bystander, A-Kaew Sae Liew, died seven months later as a result of his wounds, and three others were injured.
The Laksi incident, as it was later known, occurred in one of the hot zones during the street protests led by the since-dissolved People's Democratic Reform Committee (PDRC) that triggered the military coup by then-army commander Prayut Chan-o-cha three months later.
Mr Vivat was affiliated with the anti-election group that was trying to prevent officials from gaining access to Laksi district venues to prepare for the Feb 2 poll.