A Popular Front of India (PFI) activist was arrested in connection with the murder of local RSS leader A Sreenivasan last month.
The Pattambi-native who was held on Tuesday allegedly hacked Sreenivasan inside his shopt in the Palakkad Town on April 16.
While 16 persons are in custody in connection with political murder, the main accused and one of the three men who rode motorcycles to the crime scene are absconding.
Sreenivasan had been murdered within 24 hours of the killing of SDPI activist Subair.
The political murders had rocked the district leading to the imposing of prohibitory orders that remained in force for several days.