The Somali government says a former government worker carried out the suicide attack outside the presidential palace in Mogadishu that killed the bomber and two others.
Government spokesman Abdirahman Omar Osman said Wednesday that the attacker once worked at the presidential palace.
Former colleagues say the bomber, identified as Omar Mohamed Dhiblawe, had worked as head of the Religious Awareness Campaign at the palace.
The al-Qaida-allied group has claimed it was behind Wednesday's attack near the palace.
In an interview with VOA, Dhiblawe's wife denied her husband was an al-Shabab member and claimed he instead worked at a sesame oil factory in Mogadishu.
The United Nations-backed government pushed al-Shabab out of Mogadishu last year, but the group has vowed to continue the attacks.
Al-Shabab continues to control parts of southern and central Somalia.
The group has been fighting to overthrow Somalia's fragile transitional government and impose a strict form of Islamic law through the Horn of Africa country.
Somalia has not had a stable central government since 1991.
The country is also recovering from a severe drought and famine that displaced hundreds of thousands of Somalis.
Some information for this report was provided by AP and Reuters.