Kibera residents on Monday found bodies of five people stuffed in sacks and dumped near the railway line with some parts missing.
Police, who cordoned off the area, said they are yet to establish the motive of the killings.
One of the victims was identified as a resident of the slum who went missing on Saturday.
"The bodies were mutilated, eyes gouged out and private parts chopped off before being stuffed in a sack," an officer handling the case said.
Residents said they are living in fear following the bizzare incident and called upon the police to intensify patrols in the area.
They expressed their disappointment over the laxity of security officers saying crime has escalated during this campaign period.
