The al Qaeda-linked Islamist militant group al Shabaab, which aims to topple Somalia’s U.N.-backed government, claimed responsibility for the July 24 attack in the Somali capital.
Mayor Abdirahman Omar Osman, who previously served for a spell as a Labour Party councilor in London, died of his wounds a week later in Qatar where he was hospitalized.
"Preliminary findings show a female who worked in the local government blew herself up herself with the help of another female, who... also worked at the local government," the security ministry said in a statement carried on the state news agency.
It was al Shabaab's first known use of a disabled person as a suicide bomber and the statement suggested the bomber used her blindness to get past security and reach the mayor's offices.
The whereabouts of the blind woman's co-worker, who the ministry said was also a woman and helped her carry out the attack, was not known.
A month before the bombing, the two women took leaves of absence from work, the ministry statement said, and visited an area of Somalia controlled by al Shabaab.
"The female bomber was disabled (blind). She misused the opportunity and acted with enmity against the bosses and the people she worked with," the ministry statement said.
Osman fled as a refugee to Britain after civil war erupted in Somalia in 1991, earned a master's degree, became a naturalized citizen and worked in the housing department in the London borough of Ealing.He subsequently returned to Somalia to help rebuild his war-torn, homeland in the Horn of Africa.