Protesters marched to the offices of the IEBC
on Tuesday, demanding a speedy inquiry into the murder of IEBC acting ICT director
Chris Msando.
Msando's murder has raised fears over the legitimacy of next week's national vote.
The election board's head of information, communication and technology was tortured before he was killed, authorities said.
He oversaw the live transmission of election results, a contentious area that the opposition has said could be used to rig next Tuesday's presidential and parliamentary polls.
"It is important that security agencies expedite investigations as a matter of utmost urgency," prominent anti-corruption campaigner John Githongo said on the march, flanked by about 25 protesters.
"The timing of his torture and murder serves to undermine
Kenya's election management body," he added as the group sang and held up banners denouncing the killing.
Police found Msando's body and took it to the mortuary on Saturday, officials said. The election board announced his death on Monday.
The body had deep lacerations on the hands and arms and he had been "unmistakably" tortured, an official at the commission told Reuters.
A woman who had been shot in the head was found next to him, the official said, without identifying her.
Authorities did not say where he was found or suggest a motive.
The Opposition called for outside experts to help ensure the credibility of the elections.
"This murder has jeopardised
Kenyans' faith in the credibility of the electoral process," Musalia Mudavadi, a key ally of opposition leader Raila Odinga, told journalists.
"To restore the shaken confidence in the electronic systems that are key to the credibility and the success of the election ...the (elections body) should immediately secure the services of an internationally recognised expert in the area."
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Both the United States and Britain offered to help
Kenya
investigate the murder, without saying how.
Raila, who is standing again against incumbent President Uhuru
Kenyatta, has said the last two elections were rigged.
In 2013, he took his complaints to court and the elections were largely peaceful. But in 2007, he called for street demonstrations. The political protests and the ethnic violence that followed killed more than 1,200 people and forced another 600,000 to flee.