Why would a Muslim blow himself inside a mosque that was full of Muslims at prayer? The Qur’an forbids Muslims to kill other Muslims (4:92). But Islam has a death penalty for heretics and apostates. The jihad/martyrdom bomber may have considered that the local tribesmen, by killing a jihadi and capturing another, were “waging war against Allah and his messenger” (Qur’an 5:33), and thus deserved death.

“Suicide bomber kills at least 25 in Pakistani mosque,” by Shams Momand and Jibran Ahmad, Reuters, September 16, 2016: