48-year-old Velu was declared dead in a hospital, where he was rushed after he collapsed when police used batons to control thousands of workers who had come from different Assembly segments.
Initially, there were conflicting versions on his death as the tragedy happened at the time of police action.
Additional Commissioner of Police (Law and Order), Alok Kumar appeared to rule out the possibility of death as a result of the lathi-charge.
KPCC office premises had become a venue for protests in the recent days, with supporters of ticket aspirants holding demonstrations seeking to push their case. The Congress is yet to officially announce its list of candidates.