Pulling up in caravans of Toyota Corolla hatchbacks, dozens of them seal off mud-hut villages near the Afghan border, and then scour markets and homes in search of tribesmen they suspect of helping to identify targets for the armed U.S. drones that routinely buzz overhead.
Once they've snatched their suspect, they don't speed off, villagers say. Instead, the caravan leaves slowly, a trademark gesture meant to convey that they expect no retaliation.
Militant groups lack the ability to bring down the drones, which have killed senior Al Qaeda and Taliban commanders as well as many foot soldiers. Instead, a collection of them have banded together to form Khorasan Mujahedin in the North Waziristan tribal region to hunt for those who sell information about the location of militants and their safe houses.
Pakistani officials and tribal elders maintain that most of those who are abducted this way are innocent, but after being beaten, burned with irons or scalded with boiling water, almost all eventually "confess." And few ever come back.
One who did was a shop owner in the town of Mir Ali, a well-known hub of militant activity.
A band of Khorasan gunmen strode up to the shop owner one afternoon last fall, threw him into one of their cars and drove away, said a relative who spoke on condition of anonymity for fear of reprisal. They took him to a safe house being used as a lockup for others the group suspected of spying for the drone program.
For the next eight weeks, they bludgeoned him with sticks, trying to get him to confess that he was a drone spy. He wasn't, said the relative. Unable to determine whether he was guilty, his captors released him to another militant group, which set him free 10 days later.
"In the sky there are drones, and on the ground there's Khorasan Mujahedin," said the relative. "Villagers are extremely terrorized. Whenever there's a drone strike, within 24 hours Khorasan Mujahedin comes in and takes people away."
Most of them are killed. The group, named after an early Islamic empire that covered a large part of Central Asia, dumps the bodies on roadsides, usually with scraps of paper attached to their bloodied tunics that warn others of the consequences of spying for the U.S. Executions are often videotaped and distributed to DVD kiosks in Peshawar, northwestern Pakistan's largest city, to hammer home the message.