The four sustained injuries after being shot by police.
Four of the five men who attacked Galole Constituency tallying centre in Tana River County and stabbed one person to death have been arrested.
They sustained injuries after being shot by police while one died.
Four other people were seriously injured by the knife-wielding attackers.
The incident happened shortly after the incumbent Governor Hussein Dado and Galole MP Hassan Dukicha had left.
Mr Dado complained of having been rigged in the polls.
He claimed that about 5,000 votes had not been included in his total tally.
Mr Dado and Mr Dukicha were said to have raised the rigging claims at the county tallying centre before moving to the constituency one.
Security was later beefed up following the attack.
According to IEBC provisional results, former assistant minister Dhadho Godhana of ODM is leading with 23,702 votes against the incumbent's 21,821 votes.
In the parliamentary race, Mr Said Buya (Ford-Kenya) is ahead with 15,597 votes followed by Mr Dukicha (6,002 votes).
The attack interfered with tallying of votes.