He was portrayed excellently by Harvey Keitel.
Though he is a cop, in many ways he is but a scumbag and a bit judgmental himself (though that's besides the point). His ruthless devotion to finding out who shot Daryl Adams, without regard for evidence and facts, drives him to do some something shady and underhanded halfway into the movie. He resorts to trying to get Rodney to hurt him, in one way or the other in a sick attempt to get Strike to fess up. Even Andre, who did beat Strike a couple of times in the end, never did this. It's funny how he does nothing heroic for anyone until the very end, when he tries to get Tyrone to testify (and even this is just a faux heroic act, because he engineered the situation in the first place, by trying to get Rodney to attempt to hurt Strike). To those who are his friends though, he is affably evil so he deserves the label.