Al Shabab, which is linked to Al Qaeda, was kicked out of Somalia a decade ago. But while it has lost territory, suffered defections and been targeted by U.S. airstrikes, it has become deft in handling its operations, versatile in using guerrilla tactics and prolific in manufacturing bombs.

It has killed hundreds of people in Somalia and in neighboring Kenya.

The attack: A bus carrying university students to their campus was struck by the blast, which also injured 149 people. Among the victims were parents going to work, students heading to university, foreign engineers building roads, and shop owners.

Video: Images from the aftermath show destroyed vehicles and some of the wounded.