The government has released a comprehensive report on the attack at the Mayor's office in which Abdirahman Omar Osman and six others lost their lives.
The report now reveals that two female members of staff were responsible for the suicide bombing.
One of the staff members with special need and another, her assistant, did not go through the mandatory security check.
Al-Shabaab, an al Qaeda-affiliated terror group, claimed responsibility for the attack, saying it aimed for the UN envoy for Somalia, James Swan, who visited the office and met with the mayor and other district commissioners on the day of the bombing.
Al-Shabaab has launched many deadly attacks in Somalia targeting public places, including hotels and an airport.