Why Did the Mastermind Behind Al-Shabaab’s Garissa Massacre Attack the Same Town Where He Was a Teacher?

The mastermind behind al-Shabaab’s recent massacre of nearly 150 Christians at Garissa University College in Kenya is a former Islamic school teacher who used to teach in that very same town. But why would a former school teacher return to the town where he once taught just to lead in the brutal slaughtering of students?