Garissa governor Ali Korane was arrested over last week's shooting of former finance executive Idris Mkhtar.
Korane was apprehended by Flying Squad officers at his Nairobi home on Tuesday morning and locked up at Kilimani police station.
Two other suspects, believed to be hired assassins, were also arrested and held at Kilimani.
He had been sacked by the former Garissa County administration and moved to court where he was awarded Ksh50 million for wrongful sacking.
Mkhtar was shot while at a shopping mall in Kileleshwa and suffered serious injuries in the head.
The Director of Public Prosecutions (DPP) had ordered the Director of Criminal Investigations to immediately commence a probe to the circumstances that led to the shooting with a view of apprehending the culprits.
Last week on Wednesday, a team was set up and visited the scene of the shooting as they tried to get leads to the incident.
Five people were interrogated by the team pursuing the case amid growing tension in his home in Garissa where there were fears of inter-clan retaliations.
Police stated that a lone gunman had followed the victim to his car and shot him at close range in the head before escaping without stealing anything from him.
They, however, could not establish the motive of the shooting as a team of detectives who visited the scene were informed that Mkhtar had left prayers at a nearby mosque and was heading to his house when he was attacked.
A family spokesman claimed that the former CEC had reported of threats to his life to police. He shared his statement in which he named possible suspects behind the threats with his lawyers.
He had also received calls from a strange number that had originated from Dubai which had warned him to take care of his life over issues he had been handling in the past at the County.
