Takfir is the declaration that a fellow Muslim, by acting against Islam in some way, has become an unbeliever. Here it is in action. "Insurgents kill 3 Muslims in south of Thailand," from [1] Reuters, March 23 (thanks to Twostellas):

YALA, Thailand - Suspected insurgents shot dead three villagers, including a paramilitary guard, in Thailand's restive Muslim south, police said on Wednesday, the latest violence in the region bordering Malaysia.

At least 10 gunmen, believed to be separatist rebels, stormed a house in Narathiwat province on Tuesday night and opened fire on a Muslim couple and their neighbor as they watched television, Police Lieutenant Pairat Kiatjaroensiri said.

Among the victims was a 33-year-old defense volunteer, one of hundreds trained by the government to provide security in villages across Yala, Narathiwat and Pattani provinces, where ethnic Malay separatists are waging a bloody rebellion against the Thai state.

The paramilitary guards are often viewed as government spies and are prime targets for assassination by insurgents.