TO Umar Ohoitenan Kei, 33, his modest home in East Jakarta, is also his headquarters. One morning in October, standing next to his gate, he looked nervous, shouting to someone on the other end of his cellphone, "Why aren't the boys on their way yet?"

Half an hour later, at about 9am, dark-complexioned young men appeared, one by one. The place became busy. Hasan Basri, a tough-looking 40-year-old sporting a shaven head, took command of the group.

Insi