PESHAWAR, Pakistan — As Pakistani Taliban gunmen strode through the corridors and classrooms of the Army Public School on Tuesday, spraying teachers and pupils with bullets, one paused from his grisly work to make a phone call.

“We have killed all of the children in the auditorium,” the militant, later identified by the military as Abuzar, told his handler. “What do we do now?”

“Wait for the army to arrive,” came the reply. “Kill them, then blow yourself up.”

That conversation, recounted by a senior security official who said it had been intercepted by Pakistani intelligence, offered sobering proof of the methodical approach and cold resolve of the Taliban militants who, over the course of an eight-hour rampage, killed 148 people in the Peshawar school, at least 132 of whom were children.

On Wednesday, the horror of their actions paralyzed Pakistan, a country with much experience of Taliban atrocities and yet, in this instance, uniquely affected.