At least two persons were during the election to fill the vacant Lokoja/Kogi seat in the house of representatives.
The Independent National Electoral Commission (INEC) conducted a bye-election in the constituency on Saturday.
The exercise which started peacefully, with impressive turnout of voters, was later marred by violence.
Suspected political thugs reportedly moved from one polling unit to another to perpetrate fraud.
William Aya, spokesman of the Kogi police command, said one Yadau Umoru was killed at Ugwan Pawa polling unit in front of Maigari palace while attempting to snatch a ballot box.
He said the corpse of the deceased had been deposited in the morgue of the Federal Medical Centre, Lokoja.
An unidentified man had reportedly been killed earlier in the day by a mob at the polling unit located by Abuja Electricity Distribution Company’s office in Lokoja, while also allegedly attempting to snatch a ballot box.
Aya said the identity of the dead man was still unknown.
The All Progressives Congress (APC) and the Peoples Democratic Party (PDP) see the election as a test for 2019.