A veterinarian was shot dead by thugs as he alighted from his car to open the gate to his house in Tarabana, Limuru constituency, on Saturday night.
AP commander Thumi Gitonga said Kimani Njeng'ere was shot in the arm and the bullet penetrated through to his chest.
Residents said they heard gunshots, but did not see the culprits.
"No one witnessed the shooting. He was alone in the car. We are investigating whether he was shot while inside his car or outside. We found him lying outside his car," the AP boss said.
Police are yet to establish whether items were stolen.
Area MP Peter Mwathi appealed to Interior CS Fred Matiang'i to intensify patrols in estates.
Tarabana village neighbours the Nairobi-Nakuru highway at Kamandura.
Mwathi on Sunday said thugs flee to the highway easily after attacking residents.
He recounted how a priest - John Njoroge - was shot dead by thugs in Kinoo last week in the neighbouring Kabete constituency, 500m away from the highway.
"Our able CS should come to our areas and ensure thorough patrols are conducted. We don't want to hear such cases of people being killed with a bullet. Last time it was a priest and this time it's a businessman," Mwathi said.