The police accused Mr Onigbo of producing the locally-made bombs used in attacking police divisions.
The army claimed that the gunman was killed in an encounter at Ihioma Community in Orlu Local Government Area of the state.
The troops were met with stiff resistance from the militants as they closed in on their enclave along the Imo-Anambra border communities.
Additionally, mobile phones, laptops, as well as other weapons were allegedly recovered during the operation.
The army said its troops recovered one AK-47 rifle, one magazine containing 21 rounds of 7.62 mm special bullets and one telephone handset from Mr Nnamdi.
The army said “IPOB has continued to intimidate and harass citizens who come out to do their legitimate businesses.”
The police command said its Bomb Disposal Squad (BDS) was deployed to defuse the explosives.
Court documents, as well as viral videos, identified the suspects charged with burning Oba of Lagos palace as Yoruba living in the palace neighbourhood.
INEC spokesman Festus Okoye said it wouldn’t reach out to proscribed IPOB/ESN in its stakeholders engagement ahead of the Anambra elections.
The police in Anambra says it was still monitoring the development.
