Two gunmen were arrested on Saturday as they tried to cross into Somalia and back to Kenya through Garissa County.
Aden Hassan Mohammed (22) and Ibrahim Ali Guyo (19) were apprehended after a taxi driver drove them into a police station.
The driver, whose name was withheld for security reasons, had picked Aden and Ibrahim from Hoosingo area in Somalia.
The clients of the cab operator who was driving a Toyota Succeed wanted him to drop them in Hamey area in Somalia.
On reaching Hamey they changed and said they wanted to go to Hagadera in Kenya.
He became suspicious when they asked him to avoid highways and stick to unmanned routes.
Upon reaching the police station, the officers recovered a Marakov Zeska pistol and several rounds of ammunition.
They also found a white powdery substance which has been taken for forensic examination.
The authorities are investigating whether the two might have been involved in the Riverside attack that left 21 dead.
On Friday detectives, arraigned in court two taxi drivers suspected to have aided the Riverside attackers with movement.