Ogbonnaya Nta, spokesman of the Abia state police command, confirmed the incident to NAN, but did not give details of how Onyemachi was killed.
Nta said the deceased was a member of staff of Isialangwa north local government, venue of the election.
He added that three others sustained injuries, revealing that the command had arrested four persons in connection with the mayhem.
A witness said trouble broke out when some delegates rejected the list presented by officials who were to conduct the exercise.
He said the delegates threatened to disrupt the exercise on the grounds that the list was allegedly “doctored” to favour a particular aspirant.
The witness said in the midst of the crisis, “somebody sneaked into the chairman’s office with a jerrycan of petrol and set the place ablaze”.
“The intention was to burn the disputed list.”
The primary, which were organised to elect the party’s flag bearers for the December 17 local government election in the state, was stalemated in most of the 17 council areas due to violence.
There were also allegations of attempts by some powerful politicians to impose their “anointed’’ candidates.
Don Ubani, publicity secretary of the party, denied the allegations in a telephone interview, but admitted that there were “minor skirmishes during the exercise in some local government areas”.
Ubani said the party’s leadership was still reviewing the reports of the election committees.