I guess they have run out of people to kill, so,they're killing each other.
The killing of Abu Hayjaa al-Tunsi, a Tunisian jihadi, sparked a panicked hunt within the group's ranks for spies who could have tipped off the U.S-led coalition about his closely guarded movements. By the time it was over, the group would kill 38 of its own members on suspicion of acting as informants.