The body of the 22-year old man was found few meters away from the scene of the attack with gunshot wounds.
Police said he had tried to escape from the scene after the attack but was overwhelmed and his body was discovered almost an hour later.
Eight other people including four police officers are admitted in hospital following the 7 pm incident.
Police said the victims are in a stable condition in hospital and that two of them had been operated on.
The incident happened as the officers drove in a police car to their places of work.
Witnesses and police said unknown people threw a grenade into the police vehicle as it sped past a crowd along Ngamia Road near the local DO’s office.
One of the officers sustained injures in the head while the second one had chest injuries and a third one had leg injuries, police said. The other four were civilians who were walking near the scene of the incident.
The attack was followed by gunshots that were fired by the attackers who escaped into the crowd, police said.
North Eastern Provincial Police Officer Phillip Tuimur said no arrest had been made but police were pursuing the attackers.
The incident was the latest in a series that have happened in the area since October 2010 when Kenyan troops crossed to Somalia to hunt Al Shabaab militants.
Last Friday two people were killed and seven wounded in a grenade attack at Dagahale area, Dadaab.
Police said the blast happened when a speeding saloon car stopped at a tent where the locals use it as a place for chewing miraa, stopped and hurled a grenade at them and sped off.
It was recently reported by Garissa County Commissioner Maalim Mohammed that Al Shabaab was offering a bounty reward of up to Sh890,000 ($8,000) for any Kenyan security officer killed.
Mr Mohammed said the Government got the information after intercepting the Al Shabaab militants’ communication.
Source:- standard media