Somali National Security and Intelligence Agency (NISA) said the suspect whose identity was not disclosed staged an attack on Sunday in Mogadishu that claimed the life of Mohamed Amin Sheikh Elmi, a former secretary at Banadir administration.
NISA said the suspect was arrested at his house in Mogadishu during a security operation that also saw the officers seize phones, batteries and other bomb making materials.
Elmi succumbed to injuries he sustained following an explosion that targeted his vehicle on Sunday in the restive city.
The al-Qaida allied group which has been fighting for the overthrow of the Western-backed government claimed responsibility for the Sunday's blast.
Al-Shabab,the Somali government and African Union forces have been on major offensives against al-Shabab militants in central and southern Somali regions, but the militants still hold swaths of territory in those regions, conducting ambushes and planting roadside bombs.