He was arrested in Nairobi West where he was meeting an undercover detective planning the said murder of the witness in the case.
Police said they recovered two mobile phones from Olaba which are undergoing forensic analysis to establish if there were more players in the crime.
Olaba had apparently approached another party seeking ways of eliminating the witness in the case before police were informed.
The officers then sent undercover officers who posed as possible executors of his mission before they pounced on him.