NOVOCHERKASSK, Russia — The convoy of cars crawled along a potholed road deep in the flatlands of separatist-controlled eastern Ukraine on what was supposed to be a routine trip for a rebel leader. Instead, it ended in disaster.
First, a bomb exploded on the roadside. Then, machine-gunners opened fire on the immobilized convoy. When the ambush was over, five bodyguards, a press secretary and Aleksei B. Mozgovoi, the rebel leader, lay dead.
Rebels have been fighting in Ukraine for more than a year now, but the bloody assault this May was different: a massacre carried out by separatist rebels against another rebel group and former ally, the famed Cossacks, in a clash over the groups’ competing territorial claims.