The attack came in the week that hundreds of Boko Haram suspects went on trial at civilian courts.
The officers said Saturday the U.S. forces had thought the victims were militants.
The attackers struck during rush hour in Tayran Square, where the twin explosions also wounded at least 105 people.
The U.N. reported more than 100 civilians have been killed in airstrikes in Yemen in just the past 10 days.
The Supreme Court is declining to revive a lawsuit over a drone strike in Yemen that killed five people.
So composed were the militants that they methodically checked their victims for signs of life, shooting those who moved.
Militants assaulted a crowded mosque on Friday, blasting helpless worshipers with gunfire and rocket-propelled grenades.
Troops regained control of the Nasa-Hablod hotel on Sunday morning, killing three attackers and capturing two.
The U.S. has stepped up military involvement in Somalia, carrying out at least 19 drone strikes against al-Shabab since Janua...
The assailant blew himself up in a mosque packed with worshippers as they began their prayers.