NASA leader Raila Odinga claims anti-riot police officers killed 15 of his supporters who had turned up to welcome him on Friday after his US trip.
Raila on Saturday said he had visited the city mortuary and established police had "mercilessly terminated 15 young lives whose mistake was just to turn out and welcome their leader".
Raila was speaking at Okoa Kenya Secretariat after vising various hospitals where some of the victims of police brutality had been admitted.
"It is so unfortunate; we want to condole with all the families of the relatives. We are all mourning as a country for losing such young innocent lives to a state that has no sense to protect its citizens," he said.
Raila said, "As NASA movement we shall help with all funeral arrangements but all those who committed these heinous crimes will ultimately pay the price".
"None of you will be forgotten. You did not die in vain. You sacrificed your lives for the cause of democracy as it gave you the freedom to choose your leaders and determine the direction of your country,” he said.
Police spokesperson George Kinoti on Friday claimed five people were killed by mobs on for looting during the procession.
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Raila said Fridays' events must be condemned, adding that police brutality meted on his supporters was unnecessary since it was a peaceful procession.
The NASA leader maintained the country is currently in a political disarray as many Kenyans do not accept the legitimacy of the October 26 election.
He said another election will offer a solution to the current situation as IEBC is riddled with criminal elements who cannot allow a free, fair and credible election.
He said since they began their campaigns before the August 8 general election, President Uhuru Kenyatta and his brigade has been repeatedly accusing the NASA family of planning to cease power unlawfully.
"They have been accusing us of planning crimes of which everyone now knows they have been committing. But we want all Kenyans to know we are not going to back down on the fight for democratic change and rule of law," Raila said.