The Culling Crews were covert assassination teams, the last and dirtiest option to quietly remove threats to the global system. They were set up and run by "the People" (who became InterDep), an offshoot of various foreign intelligence services and known of only by the highest ranking of Judges. Occasionally the Chief Judges would themselves make use of the Crew setup, when they needed a problem to die and couldn't afford the comeback that might happen from a homegrown hit squad. 
In the late 2090s, the Culling Crews were created out of "biots": genetically engineered, horribly abused children (then legal under international laws) grown in Bangkok or in post-rad Manchester. An intense training and engineering program was done to make them trained killers, with other child biots turned into psi-linked biological computers ("Babes") to assist them. The mental conditioning process was developed by Harvey Glass, based off his work manipulating children with the Mimsey(TM) company. 
Known operations included the assassination of an insane Sov general after the Apocalypse War to prevent a reprisal attack; the 2106 murder of a yakuza boss's wife and son so they couldn't be used as leverage in a clan merger that threatened the Hondo City government; and the murder of Brit-Cit gangster Benny Kane in 2116, including the death of Judges who got too close. 
They were compromised along with InterDep and used to destabilise megacities before every operative bar one was killed in 2117. The megacities discussed recreating the Culling Crew to carry on removing such threats. However, they were never heard from since and their surviving operative began working for Brit-Cit's Star Chamber.
- Details were retconned or dropped between Wetworks and The Mancunian Candidate, where the main Crew member is said to be a Brit-Cit government covert op.