Collins Jumaisi was arrested last month in connection with the discovery of at least six bodies wrapped in plastic bags in Kware quarry, which is now used as a rubbish dump.
He broke out of the Gigiri police station alongside 12 Eritrean nationals, police spokesperson Resila Onyango said.
Police say Jumaisi admitted to killing 42 women including his wife, but his lawyer told a court he was tortured into making a confession. Prosecutors deny he had been mistreated.
(Reporting by Humphrey Malalo, Writing by Hereward Holland, Editing by Angus MacSwan)

The prime suspect in the Kware killings, Collins Jomaisi Khalisia (R), attends a court session at Kiambu Law Courts, Kiambu County, in Nairobi, Kenya, 16 July 2024. The head of the Criminal Investigations Directorate announced that 33-year-old Khalisia confessed to killing 42 women, including his wife, since 2022. Khalisia was apprehended on 15 July 2024 after uncovering multiple bodies wrapped in plastic bags at a quarry in Kware, Nairobi. EPA-EFE/STR