Mr Chukwu and his aide were killed by gunmen earlier in the week with several others injured.
But in his reaction, Buhari said the perpetrators have no respect for life.
Presidential aide Femi Adesina in a statement said those behind the act “deserve the wrath of natural and divine justice. The President affirms his avowed commitment to an election that is devoid of violence and rancor.
He reminds all political actors that it is the choice of the electorate that counts, and therefore all eligible Nigerians should boldly exercise their civic rights without any fear of intimidation.
‘The President directs security agencies to track down the culprits of this heinous crime, even as he commiserates with families of the victims, the Nigerian Bar Association (NBA), and the Labour Party.
‘President Buhari prays for the repose of the souls of the deceased and comfort for those who mourn.”