They want to interrigate him, ofcourse. He seems to be a single cell more or less operating on his own. It seems like he only has one gun, dosn´t look like he has any logistical support. Even simple criminals wouldn´t use the same gun twice in seperate planned attacks. The fact that he was so easy to locate also indicates that he dosn´t have logistical support, he didnt have any safehouses.
Aden hotel used by Yemen goverment hit by grenade (Reuters)