Sociopath? Definitely. Gangster? Not so much.

Despite being incredibly disturbing, Brighton Rock (directed by Rowan Joffe, originally written by Graham Greene) provides an interesting analysis of the main character, Pinkie.
The movie begins by providing background, a supposed reason for Pinkie’s insanity.  The death of Pinkie’s mentor apparently sparks a rage in him that leads him to commit murder after murder, and results in his overall instability.  Yet, the way Pinkie is portrayed suggests more than simply rage.  Had he been simply distraught and mad, it would be reasonable to suggest that the revenge killing of Fred Hale would be justified.  But other actions indicate otherwise.
The one scene in the movie that is not overtly portrayed as disturbing (oddly enough), is the scene where Pinkie lies on his bed with the spider.  Everyone is familiar with the notion that sociopaths frequently torture animals or insects at a young age, and Pinkie is no exception.  He grabs the spider hanging from the ceiling, and, pulling one leg off at a time, calmly recites: “she loves me, she loves me not.  She loves me, she loves me not.”  The torturing of the insect becomes a child’s game for him.
If this is not enough, notice one of the last scenes of the movie.  Pinkie believes that if he is to remain innocent, he would have to dispose of Rose.  Yet, the method he chooses to do so is quite disconcerting.  He decides that he should essentially trick Rose in killing herself.  Pinkie has a gun - he brings her to a secluded area, and all he has to do is point it at her and pull the trigger.  But his need to see her kill herself, to satisfy his hatred (refer to the scene with the recorder), strongly suggests sociopathy.
So with this pretty clearly established, does Pinkie act as a powerful mobster? Surely he possesses the capabilities and traits: an utter lack of remorse for killing, and strong ambition, just to name a few examples.  Greene suggests otherwise.

First is the scene in which Pinkie tries to kill Hale.  Standing behind him in the bathroom, he looks very imposing.  But as Hale keeps a calm demeanor and adeptly disarms the unsuspecting Pinkie leaving him cowering in a urinal, Pinkie is portrayed as anything but.  He is left looking like a frightened boy.  Juxtaposed with Hale, the last thing he looks like is a mobster, let alone a boss.
Time and time again, Pinkie makes bad decision after bad decision.  Just shortly after the last scene, Pinkie attempts to bargain with the Colleoni boss.  Believing he is in a position of power, he negotiates not only the death of one of his only three remaining men, but he sets himself up to be shanked as well.
Though on the surface he seems powerful, Pinkie is clearly not.  Even his handling of Rose reflects inexperience - his manipulation of her would have been unnecessary had he handled the situation differently from the very beginning.  Even though Rose clearly represents innocence, potentially Pinkie can too, in his inexperience.  This opens the movie (and Greene’s original novel) up to the interpretations of innocence: can it really be that innocence is bad in nearly every scenario? The film appears to portray its negative effects from the manipulator to the manipulated, but could there possibly be a healthy innocence in Brighton Rock?
Either way, Pinkie may be a sociopath, but he is merely a sociopathic child.