Salim Jamil Ayyash has been charged with conspiracy aimed at committing a terrorist act, committing a terrorist act by means of an explosive device, intentional homicide with premeditation by using explosive materials, intentional homicide of 21 people in addition to the intentional homicide of Mr Hariri and attempted intentional homicide of 226 others.
While the court found no evidence of direct involvement by the leadership of Hezbollah, which is backed by Iran, or the Syrian government, the judges say the killing was clearly a politically motivated act of terrorism.
The judges also ruled while they had motive, the guilt of the three other men on trial couldn't be proven beyond reasonable doubt.
Ayyash's sentence is to be decided at a later date.
The whereabouts of the four men are unknown and they were not present at the highly sensitive trial that lasted more than four years and cost around a billion dollars.
