The Supreme Court on Tuesday overruled a lower court's 10-year prison sentence given to a man charged with illegal possession of firearms and carrying them in public places without permission in connection with the political unrest in 2010.
Kittisak Soomsri, 49, was acquitted of all firearms-related charges in the ruling handed down via a video call.
The charges were related to political violence in which so-called "men in black" fired at protesters and security forces near Khok Wua intersection in Phra Nakhon district on April 10, 2010.
In the case, Mr Kittisak and Preecha Yuyen, 29, were found guilty by the Criminal Court in January 2017 and sentenced to 10 years in prison each. The three other defendants -- Ronnarit Suricha, 38; Chamnan Phakheechai, 50, and Punika Chusri, 44 -- were acquitted.
The Appeal Court upheld the 10-year prison sentences for Mr Kittisak and Mr Preecha and the acquittal for the three others. However, the court ordered the detention of those who were acquitted pending the appeal process.
Mr Kittisak was the only defendant who appealed the ruling with the Supreme Court.
The Supreme Court said it reviewed the evidence and dismissed the charge to give the defendant the benefit of the doubt. It also ordered Mr Kittisak's release.
The five were arrested in September 2014 in an investigation handled by the Department of Special Investigation.
The prosecution told the court that the five defendants and their accomplices carried firearms, ammunition and explosives -- such as an M79 grenade launcher, an M16 rifle and an HK33 rifle -- to Khok Wua intersection in Phra Nakhon district.
At that time, the United Front for Democracy against Dictatorship was staging demonstrations against the Democrat-led administration and soldiers were sent in to clear protest sites that day.
The "men in black" appeared and allegedly opened fire on the troops as well as protesters. The clash at Khok Wua intersection killed 26 people including five soldiers and one Reuters journalist.