Detectives have arrested a driver and a passenger of the ill-fated Mandera-bound bus that was ambushed by suspected militants on Friday evening.
The two have been arrested and are set to be questioned over the attack that left 11 people dead.
Eight of those who died were police officers who were on their way to their work station.
Police reports indicate that the passenger who was arrested was on his phone during most part of the journey.
According to Mandera Governor Ali Roba the attackers segregated locals from non-locals.
"I am informed that the attackers who are suspected to be Al Shabaab attacked in a cowardly segregated manner targeting non-locals heading to Mandera from Nairobi. It is extremely sad and humanly disturbing to learn that, yet again, they segregated locals from non-locals before killing those they believed to be non- locals," Roba said
Eldas Member of Parliament Adan Keynan said, "this a criminal gang that has no religion... that has no human face... that has no value at all."
The Supreme Council of Kenya Muslims (Supkem) condemned the attack indicating that the ultimate goal of the militants was to drive a wedge and cause discord between Kenyans of different faiths.
The officers bodies were moved to Gilgil while those of two civilians and a doctor were airlifted to Nairobi and kept at different morgues.
From the attack, two police officers have not been accounted for.