Additional Sessions Judge P J Vincent allowed the discharge petitions filed by the accused, holding that the evidence submitted by prosecution against them was insufficient to proceed further.
Chandrasekaran, who broke away from CPI-M, was hacked to death by a gang on May 4, 2012 at Onchiyam in the district.
Police filed the conspiracy case based on information provided by some of the accused arrested in connection with the murder case.
The court had last year convicted 12 persons in the murder case.