(Spoiler alert): the first 'H' discovered was Dot who had been groomed by the OCG. The story we're lead to believe in the last series is that there wasn't one OCG but several splinter groups still loosely in control but on basis of police incompetency, ego, laziness and how individuals are able to be corrupted with the splinter groups plans being communicated via Buckells. We didn't see anyone be groomed to be part of the police since Ryan who could have been groomed mainly by the OCG with some assistance getting him into the police by previous versions of H.
I still think that makes a lot more sense than a police officer (Kate? Hastings?) being in charge of the OCG which is one of the alternatives.