North Eastern PPO Charlton Mureithi said the suspect was arrested Saturday morning and was being interrogated by officers from the anti-terror unit.
Police have also revealed that the death toll in the bomb blast last week in Garissa is about five according to the analysis of the body parts recovered at the scene.
Among the badly mutilated parts were three legs, all left, implying that they were for three different people according to the detectives.
Another part, which did not match the other parts, was also found near the scene.
The improvised explosive device exploded when unknown persons were assembling it on a dais at Garissa Primary School grounds where an official function was to be held the following day.
But Mr Mureithi said none of the bodies had been identified.
Police also recovered three pistols, one belonging to a slain officer. -Daily Nation
