Political sources say a suspect, Krishantha Pushpakumara, is planning to make a statement to the court implicating prime minister Ranil Wickremesinghe in the incident.
The clash occurred between groups supporting Wickremesinghe and demanding his resignation from the party leadership.
Pushpakumara had been in the group that supported the UNP leader, and was shot at during the clash.
A few months later, he joined the SLFP, and is presently a Mahinda faction member of the southern provincial council.
Mahinda is using him
Political sources say ex-president Mahinda Rajapaksa is using Pushpakumara to implicate Wickremesinghe in the clash.
Pushpakumara will tell the court that the group including him attacked the anti-Wickremesinghe protestors with the knowledge and on the advice of the UNP leader.
Sixty UNP members, including minister Mangala Samaraweera, are accused in this case.
Rajapaksa had tried in the past few days to get the support of certain other suspects to implicate Wickremesinghe, the sources add.