My only problem is they go to the ONE cop who's in on it/aware?

I suspect that she's carefully positioned herself as the one investigating the missing persons cases (even though she never gets anywhere) so that anything related to it has to go through her, and she can cover up anything that might expose the conspiracy. And who says she's the only one? For all we know, there could be quite a few cops in on it.

Who says she's the only one. She's the only one two people in a film in one district run into.

If I'm correct the story had the "father's" run the new York so one cop under their control isn't that unbelievable.

There was more than one cop that was aware of what was going on, for the sake of the movie they're just going to show one cop though. Odds are that they would of eventually been given a lot of excuses and bs about the missing people and Mahogany.

I love you guys... eh, screw you guys.

What about the cop who demanded to check Leon's camera as he photographed Mahogany in the subway? I don't believe that that was merely a coincidence.