Five CPI-M and one Trinamool Congress worker were killed on January 25, 2000 at Chakgobindapur and Madhupur villages in an armed clash over area dominance.
Seventh Additional judge of Midnapore court Prasad Kumar Ray acquitted and released the accused for want of evidence.
Ninety nine people had been named accused by CPI-M in a complaint to the police who chargesheeted 18 of them.
During the trial of the case, one of the accused died.
The judgement today acquitted and released the rest 17.